Image processing apparatus and image processing method

ABSTRACT

Image processing apparatus and image processing method for formation of high quality image by high-speed error diffusion processing by execution of more complicated threshold condition processing in a simple manner. When error diffusion processing is performed on multivalued image data having plural density components and the result of processing is outputted, upon execution of error diffusion processing on a first density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of a second density component, then the error diffusion processing is performed on the first density component based on the determined threshold value, and the result of execution of the error diffusion processing is outputted. Further, upon execution of the error diffusion processing on the second density component among the plural density components, a threshold value used in the error diffusion processing is determined based on a density value of the first density component, then the error diffusion processing is performed on the second density component based on the determined threshold value, and the result of the error diffusion processing is outputted.

FIELD OF THE INVENTION

[0001] The present invention relates to an image processing apparatusand an image processing method, and more particularly, to an imageprocessing apparatus and an image processing method forpseudo-halftoning by performing error diffusion processing onmultivalued image density data.

BACKGROUND OF THE INVENTION

[0002] Conventionally, the error diffusion method is known aspseudo-halftoning to represent a multivalued image in binaryrepresentation (See “An Adaptive Algorithm for Spatial Gray Scale” inSociety for Information Display 1975 Symposium Digest of TechnicalPapers, 1975, pp. 36). According to this method, assuming that a pixelof interest is P and its density is v, densities of adjacent pixels P0to P3 of the pixel of interest P, v0 to v3, and a threshold value forbinarization is T, a binarization error E in the pixel of interest P isdistributed by empirically obtained weighting coefficients W0 to W3 intothe adjacent pixels P0 to P3 so that a mean density is macroscopicallyequal to an original image density.

[0003] For example, when the value of output binary data is “o”,

[0004] If v≧T holds, o=1, E=v−Vmax; . . . (1)

[0005] If v<T holds, o=0, E=v−Vmin;

[0006] (Vmax: maximum density, Vmin: minimum density)

[0007] v0=v0+E×W0; . . . (2)

[0008] v1=v1+E×W1; . . . (3)

[0009] v2=v2+E×W2; . . . (4)

[0010] v3=v3+E×W3; . . . (5)

[0011] (Example of weighting coefficients: W0={fraction (7/16)},W1={fraction (1/16)}, W2={fraction (5/16)}, W3={fraction (3/16)})

[0012] Conventionally, when a multivalued image is outputted by a colorink-jet printer or the like using 4 color inks of cyan (C), magenta (M),yellow (Y) and black (K), the pseudo-halftoning is performed by usingthe error diffusion method or the like for each color. Regarding eachcolor, the processing provides an excellent visual characteristic,however, regarding overlapped two or more colors, does not alwaysprovide such a excellent visual characteristic.

[0013] To solve this problem, Japanese Published Unexamined PatentApplication Nos. Hei 8-279920 and Hei 11-10918 disclose halftoning toobtain an excellent visual characteristic even in overlapped two or morecolors by using the error diffusion method for combination of two ormore colors.

[0014] Further, Japanese Published Unexamined Patent Application No. Hei9-139841 discloses similar improvement by performing pseudo-halftoningindependently on two or more colors and then correcting output values bythe sum of input values.

[0015] Especially, to reduce graininess of intermediate density area ofcolor image, it is effective to perform image formation avoiding overlapbetween cyan (C) component and magenta (M) component, and for thispurpose, the following method is employed.

[0016]FIG. 24 shows image formation control according to a conventionalink-jet method.

[0017] In this figure, image data is multivalue data where each densitycomponent (YMCK) of each pixel is represented as 8-bit data (0-255gray-scale value).

[0018] Assuming that densities of C and M components of original imageare C and M, densities Ct and Mt of the C and M components of pixel ofinterest in the multivalue color image are represented as follows.

[0019] Ct=C+Cerr

[0020] Mt=M+Merr

[0021] Cerr and Merr are error-diffused values of the C and M componentswith respect to the pixel of interest.

[0022] As shown in FIG. 24, regarding C and M image formation, 4 typesof image formation controls are performed in accordance with thedensities of the C and M components of the pixel of interest.

[0023] 1. If the sum of (Ct+Mt) is equal to or less than a thresholdvalue (Threshold1), i.e., the value belongs to an area (1) in FIG. 24,dot printing is not performed using C or M inks.

[0024] 2. If the sum of (Ct+Mt) is greater than the threshold value(Threshold1) and the sum of (Ct+Mt) is less than another threshold value(Threshold2), and Ct>Mt holds, i.e., the value belongs to an area (2) inFIG. 24, dot printing using only the C ink is performed.

[0025] 3. If the sum of (Ct+Mt) is greater than the threshold value(Threshold1) and the sum of (Ct+Mt) is less than the other thresholdvalue (Threshold2), and Ct≦Mt holds, i.e., the value belongs to an area(3) in FIG. 24, dot printing is performed using only the M ink.

[0026] 4. If the sum of (Ct+Mt) is equal to or greater than the otherthreshold value (Threshold2), i.e., the value belongs to an area (4) inFIG. 24, dot printing is performed using the C and M inks.

[0027] Note that Threshold1<Threshold2 holds.

[0028] However, in the above conventional art, as the image formationfor the C and M components differs in accordance with the sum of thedensity values of the C and M components, the image formation controlmust be simple. If pixels where image data to be processed changes priornear a threshold value are adjacent to each other, a pixel where the Cink and the M ink overlap with each other and a pixel where these inksdo not overlap with each other mixedly appear in the narrow area, and asa result, the quality of image formation is degraded.

[0029] To prevent the degradation of image quality, more complicatedthresholds may be employed. However, the threshold condition processingmust be more complicated, and processing time is prolonged.

[0030] Further, since the conventional threshold processing must beinevitably simple in the processing based on the sum of the densityvalues of the C and M components, flexible processing cannot beperformed without difficulty.

[0031] Further, if exclusive error diffusion is to be performed by usingthe sum of three components including the black (K) component, theprocessing becomes very complicated as represented in the followingcode. Ct=C+Cerr Mt=M+Merr Kt=K+Kerr If (Ct+Mt+Kt>Threshold1) If(Ct+Nt+Kt<Threshold2) If (Ct>Mt&&Ct>Kt) Print C Else If (Mt>Ct&&Mt>Kt)Print M Else Print K Else If (Ct+Mt+Kt<Threshold 3) If (Ct<Mt&&Ct>Kt)Print M Print K Else If (Mt<Ct&&Mt<Kt) Print C Print K Else Print CPrint M Else Print C Print M Print K

[0032] Further, in the above conventional art, the input multivaluedimage data is merely binarized by each color component and subjected tothe error diffusion processing as the pseudo-halftoning. On the otherhand, in accordance with the progress of color image printing technologyby the ink-jet method, some ink-jet printers can handle multivaluedimage data for color image printing by drop modulation or use ofsame-color thick and thin inks.

[0033] Accordingly, it is desirable to apply multivalue error diffusionprocessing to the above ink-jet printer. However, in the multivalueerror diffusion processing, as the threshold condition processing is socomplicated, if the processing is applied to an actual printer, thereduction of printing speed is conceivable. For this reason, uponapplication of the multivalue error diffusion processing to an ink-jetprinter to handle multivalued image data, a processing method capable ofmaintaining a high processing speed is desirable.

[0034] Further, as in the case of the above conventional art, in imageformation by completely and exclusively arranging C component and Mcomponent dots, in an original image having respectively 50% C and Mcomponent, all the pixels are filled with C ink dots or M ink dots,ideally, as shown in FIG. 25A. In this state, if C-ink dot positions andM-ink dot positions are relatively shifted from each other for somereason as shown in FIG. 25B, the image has pixels where C-ink dot andM-ink dot overlap with each other (bluish pixels) and blank pixelswithout dot throughout most of the image.

[0035] Accordingly, in printing by an ink-jet printer using a printheadwhere C-ink nozzles and M-ink nozzles are arrayed in a scan direction ofa carriage of the printer, a formed image periodically changes inaccordance with the position of the carriage in the scan direction byvariation in carriage scan speed or the like, as shown in FIGS. 25A and25B, and it looks to a human eye that the density of corresponding areaperiodically changes due to the variation in probability of occurrenceof blank pixels. In other words, to a human eye, the printed resultappears as a low-quality image.

[0036] On the other hand, if C-ink dots and M-ink dots are independentlyarranged in an image formation, in an original image having respectively50% C and M components as in the above case, blank pixels, pixelsprinted only with the C ink, pixels printed only with the M ink, andpixels printed with both the C and M inks are formed respectively at 25%occurrence uniformly in the formed image, ideally, as shown in FIG. 26A.

[0037] In the independent arrangement of C-ink dots and M-ink dots, apixel to be printed only with the C ink may overlap with an adjacentpixel to be printed with the M ink, as shown in FIG. 26B, on the otherhand, there is a probability that a pixel to be printed with both the Cand M inks is printed with only the C ink or the M ink. Thus, theoverall density change is small in comparison with the exclusivearrangement of C-ink and M-ink dots.

[0038] Accordingly, it is understood that the exclusive arrangement ofC-ink and M-ink dots has a problem that the uniformity of image isdegraded from intermediate to high density areas in view of a trade-offbetween the effect of reduction of graininess in a highlight portion andimage formation accuracy. If only the highlight portion is taken intoconsideration, as respective dots are initially arranged sufficientlyaway from each other, the degradation of image quality due to shift ofdot positions is very little and the advantage of the exclusivearrangement is rather greater.

SUMMARY OF THE INVENTION

[0039] Accordingly, it is an object of the present invention to providean image processing apparatus and an image processing method capable of(1) forming a high quality image by performing high-speed errordiffusion processing by performing more complicated threshold conditionprocessing in a simple manner; (2) forming a high quality image at ahigh speed while using multivalue error diffusion processing; and (3)forming a high quality image by performing optimum pixel arrangement inaccordance with image density.

[0040] According to one aspect of the present invention, the foregoingobject is attained by providing an image processing apparatus forperforming error diffusion processing on multivalued image data havingplural density components and outputting the result of the errordiffusion processing, comprising: first determination means for, uponexecution of the error diffusion processing on a first density componentamong the plural density components, determining a threshold value usedin the error diffusion processing based on a density value of a seconddensity component; first error diffusion execution means for executingthe error diffusion processing on the first density component based onthe threshold value determined by the first determination means; firstoutput means for outputting the result of execution of the errordiffusion processing by the first error diffusion execution means;second determination means for, upon execution of the error diffusionprocessing on the second density component among the plural densitycomponents, determining a threshold value used in the error diffusionprocessing based on a density value of the first density component;second error diffusion execution means for performing the errordiffusion processing on the second density component based on thethreshold value determined by the second determination means; and secondoutput means for outputting the result of execution of the errordiffusion processing by the second error diffusion execution means.

[0041] It is preferable that the first and second determination meansuse a table showing a relation between density and threshold values, fordetermining the threshold values.

[0042] It may be arranged such that the first and second determinationmeans respectively determine plural threshold values for N-aryconversion as well as binarization. In this case, it is preferable thatthe first and second determination means respectively use plural tablesfor determining the plural threshold values.

[0043] Further, it may be arranged such that the apparatus furthercomprises: third determination means for, upon execution of the errordiffusion processing on a third density component among the pluraldensity components, determining a threshold value used in the errordiffusion processing based on the sum of the density values of the firstand second density components; third error diffusion execution means forexecuting the error diffusion processing on the third density componentbased on the threshold value determined by the third determinationmeans; and third output means for outputting the result of execution ofthe error diffusion processing by the third error diffusion executionmeans.

[0044] In this manner, it is preferable that in a case where the errordiffusion processing is performed on the first to third densitycomponents, the first determination means determines the threshold valueused in the error diffusion processing on the first density component,based on the sum of the density value of the second density componentand a density value of the third density component, and the seconddetermination means determines the threshold value used in the errordiffusion processing on the second density component, based on the sumof the density value of the first density component and the densityvalue of the third density component.

[0045] Note that the plural density components are a yellow component, amagenta component, a cyan component and a black component, and the firstdensity component is the cyan component, the second density component isthe magenta component, and the third density component is the blackcomponent.

[0046] Further, it is preferable that the apparatus further comprisesimage formation means such as an ink-jet printer for inputting the errordiffusion processing results outputted from the first, second and thirdoutput means and performing image formation.

[0047] It is preferable that the ink-jet printer has an ink-jetprinthead that discharges ink by utilizing thermal energy, and theink-jet printhead has electrothermal transducers for generating thethermal energy to be supplied to the ink.

[0048] According to another aspect of the present invention, theforegoing object is attained by providing an image processing method forperforming error diffusion processing on multivalued image data havingplural density components and outputting the result of the errordiffusion processing, comprising: a first determination step of, uponexecution of the error diffusion processing on a first density componentamong the plural density components, determining a threshold value usedin the error diffusion processing based on a density value of a seconddensity component; a first error diffusion execution step of executingthe error diffusion processing on the first density component based onthe threshold value determined at the first determination step; a firstoutput step of outputting the result of execution of the error diffusionprocessing at the first error diffusion execution step; a seconddetermination step of, upon execution of the error diffusion processingon the second density component among the plural density components,determining a threshold value used in the error diffusion processingbased on a density value of the first density component; a second errordiffusion execution step of performing the error diffusion processing onthe second density component based on the threshold value determined atthe second determination step; and a second output step of outputtingthe result of execution of the error diffusion processing at the seconderror diffusion execution step.

[0049] According to still another aspect of the present invention, theforegoing object is attained by providing a computer readable storagemedium for storing a program for executing the above image processingmethod.

[0050] In accordance with the present invention as described above, whenerror diffusion processing is performed on multivalued image data havingplural density components and the result of processing is outputted,upon execution of the error diffusion processing on the first densitycomponent among the plural density components, a threshold value to beused in the error diffusion processing is determined based on thedensity value of the second density component, then the error diffusionprocessing is executed on the first density component based on thedetermined threshold value, and the result of execution of theprocessing is outputted. Further, upon execution of the error diffusionprocessing on the second density component among the plural densitycomponents, a threshold value to be used in the error diffusionprocessing is determined based on the density value of the first densitycomponent, then the error diffusion processing is executed on the seconddensity component based on the determined threshold value, and theresult of execution of the processing is outputted.

[0051] According to still another aspect of the present invention, theforegoing object is attained by providing an image processing apparatusfor performing error diffusion processing on multivalued image datahaving plural density components and outputting the result of the errordiffusion processing, comprising: calculation means for calculating thesum and difference between density values of the first density componentand second density component among the plural density components; M-aryconversion means for converting the sum value into M-ary code by using afirst function based on the sum; N-value conversion means for convertingthe difference value into N-ary code by using a second function based onthe difference; and execution means for executing multivalue errordiffusion processing respectively on the first and second densitycomponents, based on the result of conversion by the M-ary conversionmeans and the result of conversion by the N-ary conversion means.

[0052] Note that M and N are respectively a positive integer equal to orgreater than 3.

[0053] Further, it is preferable that the first function used in theM-ary conversion means is represented in a first table showing arelation between the sum value and an M-ary code, and the secondfunction used in the N-ary conversion means is represented in a secondtable showing a relation between the difference value and an N-ary code.

[0054] Further, it is preferable that the multivalue error diffusionprocessing is executed by the execution means by using a two-dimensionaltable with the result of the conversion by the M-ary conversion meansand the result of the conversion by the N-ary conversion means asfunctions. It may be arranged such that the two-dimensional table is acommon table for the first and second density components, otherwise, thetwo-dimensional table is prepared respectively for the first and seconddensity components.

[0055] In the above case, the plural density components are a yellowcomponent, a magenta component, a cyan component and a black component,and the first density component is the cyan component, and the seconddensity component is the magenta component.

[0056] Further, it is preferable that the apparatus further comprisesimage formation means such as an ink-jet printer for inputting the errordiffusion processing results and performing image formation.

[0057] It is preferable that the ink-jet printer has an ink-jetprinthead that discharges ink by utilizing thermal energy, and theink-jet printhead has electrothermal transducers for generating thethermal energy to be supplied to the ink.

[0058] According to still another aspect of the present invention, theforegoing object is attained by providing an image processing method forperforming error diffusion processing on multivalued image data havingplural density components and outputting the result of the errordiffusion processing, comprising: a calculation step of calculating thesum and difference between density values of first density component andsecond density component among the plural density components; an M-aryconversion step of converting the sum value into M-ary code by using afirst function based on the sum; an N-ary conversion step of convertingthe difference value into N-ary code by using a second function based onthe difference; and an execution step of executing multivalue errordiffusion processing respectively on the first and second densitycomponents, based on the result of conversion at the M-ary conversionstep and the result of conversion at the N-ary conversion step.

[0059] According to still another aspect of the present invention, theforegoing object is attained by providing a computer readable storagemedium for storing a program for executing the above image processingmethod.

[0060] In accordance with the present invention as described above, whenerror diffusion processing is performed on multivalued image data havingplural density components and the result of the error diffusionprocessing is outputted, the sum and the difference between the densityvalue of the first density component and that of the second densitycomponent among the plural density components are calculated, the sumvalue is converted into M-ary code by using the first function based onthe sum, while the difference value is converted into N-ary code byusing the second function based on the difference. Then multivalue errordiffusion processing is performed on the first density component and thesecond density component based on the results of the M-ary conversionand the N-ary conversion.

[0061] According to still another aspect of the present invention, theforegoing object is attained by providing an image processing apparatusfor performing error diffusion processing on multivalued image datahaving plural density components and outputting the result of the errordiffusion processing, comprising: analysis means for examining densityvalues of a first density component and a second density component amongthe plural density components; and control means for exclusively orindependently outputting the result of the error diffusion processing onthe first density component and that of the error diffusion processingon the second density component, in accordance with the result ofanalysis by the analysis means, wherein if at least one of the first andsecond density components has an intermediate density value, the controlmeans independently outputs the results of the error diffusionprocessing, while if the first and second density components do not havean intermediate density value, exclusively outputs the results of theerror diffusion processing.

[0062] It may be arranged such that the analysis means includes: firstcomparison means for comparing the sum of the density values of thefirst and second density components among the plural density componentswith a predetermined threshold value; and second comparison means forcomparing the density value of the first density component and thedensity value of the second density component with each other, and thatthe control means performs printing by the error diffusion processingbased on the first density component or the second density component,based on the results of comparison by the first and second comparisonmeans.

[0063] Further, it is preferable that the apparatus further comprisesthird comparison means for comparing the density value of the firstdensity component with the predetermined threshold value, and thecontrol means further determines whether or not printing by the errordiffusion processing is to be performed not only based on the firstdensity component, but also based on the result of comparison by thethird comparison means.

[0064] Otherwise, it is preferable that the apparatus further comprisesfourth comparison means for comparing the density value of the seconddensity component with the predetermined threshold value, and thecontrol means further determines whether or not printing by the errordiffusion processing is to be performed not only based on the seconddensity component, but also based on the result of comparison by thefourth comparison means.

[0065] In the above case, the plural density components are a yellowcomponent, a magenta component, a cyan component and a black component,and the first density component is the cyan component, and the seconddensity component is the magenta component.

[0066] It may be arranged such that the plural density components of themultivalued image data are respectively binarized by the error diffusionprocessing, otherwise, the plural density components of the multivaluedimage data are respectively converted into N-ary code (N≧3 positiveinteger) by the error diffusion processing. Further, it may be arrangedsuch that the apparatus further comprises a table showing relationbetween a density value and an N-ary code output value, for the N-aryconversion. It may be arranged such that the table is a common table forthe first and second density components, otherwise, the table isprepared respectively for the first and second density components.

[0067] Further, it is preferable that the apparatus further comprisesimage formation means such as an ink-jet printer for inputting theresult of execution of the error diffusion processing and performingimage formation.

[0068] It is preferable that the ink-jet printer has an ink-jetprinthead that discharges ink by utilizing thermal energy, and theink-jet printhead has electrothermal transducers for generating thethermal energy to be supplied to the ink.

[0069] Note that the intermediate density is higher than anapproximately half level of a maximum density level.

[0070] According to still another aspect of the present invention, theforegoing object is attained by providing an image processing method forperforming error diffusion processing on multivalued image data havingplural density components and outputting the result of the errordiffusion processing, comprising: an analysis step of examining densityvalues of a first density component and a second density component amongthe plural density components; and a control step of exclusively orindependently outputting the result of the error diffusion processing onthe first density component and that of the error diffusion processingon the second density component, in accordance with the result ofanalysis at the analysis step, wherein at the control step, if at leastone of the first and second density components has an intermediatedensity value, the results of the error diffusion processing areindependently outputted, while if the first and second densitycomponents do not have an intermediate density value, the results of theerror diffusion processing are exclusively outputted.

[0071] According to still another aspect of the present invention, theforegoing object is attained by providing a computer-readable storagemedium holding a program for execution of the above-described imageprocessing method.

[0072] In accordance with the present invention as described above, whenerror diffusion processing is performed on multivalued image data havingplural density components and the result of processing is outputted, thedensity value of the first density component and that of the seconddensity component among the plural density components are examined, andin accordance with the result of analysis, the results of errordiffusion processing on the first and second density components areexclusively outputted unless the density components of the first andsecond density component have intermediate densities, otherwise,independently outputted if at least one of the first and second densitycomponents has an intermediate density.

[0073] The invention is particularly advantageous since the errordiffusion processing is performed in consideration of the value ofanother density component, image formation in consideration of overlapwith another component is possible, and a high quality image can beformed.

[0074] Further, as the threshold used in the error diffusion processingis determined by using a table, the error diffusion processing can beperformed at a high speed by performing more complicated thresholdcondition processing in a simple manner.

[0075] Further, when error diffusion processing is performed onmultivalued image data having plural density components and the resultof processing is outputted, the sum and difference between the densityvalue of the first density component and that of the second densitycomponent among the plural density components are calculated, and thesum value is converted into M-ary code by using the first function basedon the sum, while the difference value is converted into N-ary code byusing the second function based on the difference. Then based on theresults of M-ary and N-ary conversion, the multivalue error diffusionprocessing is performed on the first and second density components.Accordingly, complicated threshold condition processing accompanying themultivalue error diffusion processing becomes unnecessary due torepresenting the first and second functions in the form of table,introducing the tables into the multivalue error diffusion processing,and performing the error diffusion processing by referring to thesetables. Thus the multivalue error diffusion processing can be performedat a high speed.

[0076] Further, when error diffusion processing is performed onmultivalued image data having plural density components and the resultof processing is outputted, the density value of the first densitycomponent and that of the second density component among the pluraldensity components are examined, and in accordance with the result ofanalysis, the results of error diffusion processing on the first andsecond density components are exclusively outputted unless the densitycomponents of the first or second density component have intermediatedensities, otherwise, independently outputted if at least one of thefirst and second density components has an intermediate density.Accordingly, the graininess from highlight to intermediate density areasin the image can be reduced, and the uniformity of the image can bemaintained from the intermediate to high density areas, thus a highquality image can be formed.

[0077] Other features and advantages of the present invention will beapparent from the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame name or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

[0079]FIG. 1 is a block diagram showing a schematic configuration of aninformation processing system according to a common embodiment of thepresent invention;

[0080]FIG. 2 is a block diagram showing a hardware construction of hostdevice 51 and that of image output device 52 constructing theinformation processing system;

[0081]FIG. 3 is a perspective view of an ink-jet printer IJRA as atypical embodiment of the image output device 52;

[0082]FIG. 4 is a block diagram showing a software construction used inthe information processing system;

[0083]FIG. 5 is a flowchart showing the outline of image processing;

[0084]FIG. 6 is a flowchart showing image formation control according toa first embodiment of the present invention;

[0085]FIGS. 7A to 7C are diagrams showing threshold conditions used inthe first embodiment;

[0086]FIGS. 8A to 8C are diagrams showing other threshold conditionsused in the first embodiment;

[0087]FIGS. 9A to 9D are diagrams showing examples of applicable variousthreshold conditions;

[0088]FIG. 10 is a flowchart showing the image formation controlaccording to a second embodiment of the present invention;

[0089]FIGS. 11A to 11C are diagrams showing threshold conditions used inthe second embodiment;

[0090]FIGS. 12A to 12C are diagrams other threshold conditions used inthe second embodiment;

[0091]FIG. 13 is a flowchart showing the image formation controlaccording to a third embodiment of the present invention;

[0092]FIG. 14 is a flowchart showing the image formation controlaccording to a fourth embodiment of the present invention;

[0093]FIG. 15 is a diagram showing threshold conditions used in thefourth embodiment;

[0094]FIG. 16 is a flowchart showing the image formation controlaccording to a fifth embodiment of the present invention;

[0095]FIG. 17 is a diagram showing threshold conditions used in thefifth embodiment;

[0096]FIG. 18 is a diagram showing a two-dimensional common table for Cand M components used in the fifth embodiment;

[0097]FIGS. 19A to 19B are diagrams showing two-dimensional tablesspecialized for the C and M components;

[0098]FIG. 20 is a flowchart showing the image formation controlaccording to a sixth embodiment of the present invention;

[0099]FIG. 21 is a diagram showing threshold conditions used in thesixth embodiment;

[0100]FIG. 22 is a flowchart showing the image formation controlaccording to a seventh embodiment of the present invention;

[0101]FIG. 23 is a diagram showing threshold conditions used in theseventh embodiment;

[0102]FIG. 24 is a diagram showing the image formation control accordingto the conventional ink-jet method;

[0103]FIGS. 25A and 25B are diagrams showing image formation byexclusively arranging the C and M components; and

[0104]FIGS. 26A to 26B are diagrams showing image formation byindependently arranging the C and M components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0105] Preferred embodiments of the present invention will now bedescribed in detail in accordance with the accompanying drawings.

Common Embodiment

[0106] First, the outline of a common information processing system usedin the following embodiments, the outline of hardware construction, theoutline of software construction and the outline of image processingwill be described.

[0107]FIG. 1 is a block diagram showing a schematic configuration of theinformation processing system according to a common embodiment of thepresent invention.

[0108] As shown in FIG. 1, the information processing system has a hostdevice 51 comprising a personal computer or the like, and an imageoutput device 52 comprising a printer or the like, interconnected via abidirectional interface 53. Driver software 54, to which the presentinvention is applied, is loaded into a memory of the host device 51.

[0109] 1. Hardware Construction of Host Device 51 and Image OutputDevice 52

[0110] Next, the hardware construction of the host device 51 and that ofthe image output device 52 will be described.

[0111]FIG. 2 is a block diagram showing the hardware construction of thehost device 51 and that of the image output device 52 constructing theinformation processing system.

[0112] As shown in FIG. 2, the host device 51, having a processor 1000and its peripheral devices, serves as a host device. Further, the imageoutput device 52 has a driving portion including a printhead 3010, acarrier (CR) motor 3011 to drive a carrier to move the printhead 3010, alinefeed motor 3012 to feed paper and the like, and a control circuit3013.

[0113] The processor 1000 of the host device 51 includes an MPU 1001which controls the overall operation of the host device in accordancewith a control program, a bus 1002 which interconnects systemconstituent elements, a DRAM 1003 for temporarily storing programsexecuted by the MPU 1001 and data, a bridge 1004 which connects thesystem bus, the memory bus and the MPU 1001, and a graphic adapter 1005having a control function to display graphic information on a displaydevice 2001 such as a CRT.

[0114] Further, the processor 1000 has an HDD controller 1006 whichserves as an interface between the processor and an HDD device 2002, akeyboard controller 1007 which serves as an interface between theprocessor and a keyboard 2003, and a communication I/F 1008 as aparallel interface for communication between the processor and the imageoutput device 52 according to the IEEE 1284 standards.

[0115] Further, the processor 1000 is connected, via the graphic adapter1005, to the display device 2001 (CRT in this embodiment) which displaysgraphic information and the like for an operator. Further, the processor1000 is connected, via respective controllers, to the hard disk drive(HDD) device 2002 as a large capacity storage device holding programsand data and the keyboard 2003.

[0116] On the other hand, the control circuit 3013 of the image outputdevice 52 has an MCU 3001, having a control program execution functionand a peripheral device control function, which controls the overalloperation of the image output device main body 52, a system bus 3002which interconnects the respective constituent elements of the controlcircuit, and a gate array (G.A.) 3003 including mechanisms to supplyprint data to the printhead 3010, to perform memory address decoding,and to generate a control pulse to the carrier motor and the like, as acontrol circuit.

[0117] Further, the control circuit 3013 has a ROM 3004 for storing thecontrol programs executed by the MCU 3001, host print information andthe like, a DRAM 3005 for storing various data (image print information,print data to be supplied to the printhead and the like), acommunication I/F 3006 as a parallel interface for communication betweenthe control circuit and the host device 51 according to the IEEE 1284standards, and a head driver 3007 which converts a head print signaloutputted from the gate array 3003 into an electric signal to drive theprinthead 3010.

[0118] Further, the control circuit 3013 has a CR motor driver 3008which converts the carrier motor control pulse outputted from the gatearray 3003 into an electric signal to actually drive the carrier (CR)motor 3011, and an LF motor driver 3009 which converts a linefeed motorcontrol pulse outputted from the MCU 3001 into an electric signal toactually drive the linefeed motor.

[0119] Next, a particular structure of the image output device 52 willbe described.

[0120]FIG. 3 is a perspective view of an ink-jet printer IJRA as atypical embodiment of the image output device 52.

[0121] In FIG. 3, a carriage HC is engaged with a spiral groove 5004 ofa lead screw 5005 which rotates via drive force transmission gears 5009to 5011 interlocking with forward/reverse rotation of a driving motor5013. The carriage HC has a pin (not shown) and it reciprocates indirections indicated by arrows a and b, held by a guide rail 5003. Thecarriage HC has an ink-jet cartridge IJC which integrally comprises aprinthead IJH and an ink tank IT. A paper holding plate 5002 presses aprint sheet P against a platen 5000 along the moving direction of thecarriage HC. Photocouplers 5007 and 5008 are home position detectingmembers for checking the existence of lever 5006 of the carriage in thisarea and changing over the rotational direction of the motor 5013. Asupport member 5016 supports a cap member 5022 for capping the frontsurface of the printhead IJH. A suction member 5015 performssuction-recovery of the printhead by sucking the inside of the capmember 5022 via a cap inner opening 5023. Member 5019 allows a cleaningblade 5017 to move in back-and-forth directions. A main body supportplate 5018 supports the member 5019 and the cleaning blade 5017. It isapparent that any well-known cleaning blade is applicable to the printerof the embodiment. Numeral 5021 denotes a lever for starting the suckingoperation of the suction-recovery. The lever 5021 moves along themovement of a cam 5020 engaged with the carriage HC. A well-knowntransmission mechanism such as clutch change over controls a drive forcefrom the driving motor.

[0122] When the carriage HC is at the home position area, a desired oneof these capping, cleaning and suction-recovery is executed at itscorresponding position by the lead screw 5005. The timing of any ofthese processings is not limited to the printer of the embodiment, if adesired processing is performed at a well-known timing.

[0123] Note that as described above, the ink tank IT and the printheadIJH may be integrally formed as an exchangeable ink cartridge IJC.Further, it may be arranged such that the ink tank IT and the printheadIJH can be separated, and when ink is exhausted, only the ink tank IT isexchanged for new one.

[0124] Further, the control circuit described above with reference toFIG. 2 is included in the ink-jet printer IJRA.

[0125] The printhead IJH prints a color image by using at least fourcolor inks of yellow (Y), magenta (M), cyan (C) and black (K) based onmultivalued density data of respective YMCK components.

[0126] 2. Outline of Software Construction and Outline of ImageProcessing

[0127]FIG. 4 is a block diagram showing the software construction usedin the above-described information processing system.

[0128] As it is understood from FIG. 4, to output print data to theimage output device 52, the host device 51 performs image processing bycollaborated operation among application software, an operating systemand driver software in a layer structure.

[0129] In the present embodiment, processings individually depending onthe image output devices are handled by device-specific drawingfunctions 31-1, 31-2, . . . , 31-n, separated from a program forgenerally executing programs depending on individual implementations ofimage processing apparatus. Further, the core processing of driversoftware is independent of the individual image output devices.

[0130] A line-segmented image converted into a quantized amount issubjected to image processing by a color characteristic conversionmodule 33, a halftoning module 34 and the like. Further, a print commandgeneration module 35 adds a command to the data and compresses the data,and delivers the generated data to the image output device 52 via aspooler 22 provided in the OS (Operating System).

[0131] As shown in FIG. 4, application software 11 is provided in thelayer of application software, and a drawing processing interface 21which receives a drawing command from the application software 11 andthe spooler 22 which delivers the generated image data to the imageoutput device 52 such as an ink-jet printer are provided in the layer ofthe OS (Operating System).

[0132] Then, the device-specific drawing functions 31-1, 31-2, . . . ,31-n holding representation formats specific to the image outputdevices, the color characteristic conversion module 33 which receivesline-segmented image information from the OS and which converts thecolor representation in the driver to a device-specific colorrepresentation, a halftoning module 34 which performs conversion toquantized amounts for representing respective pixel states of thedevice, and the print command generation module 35 which adds a commandto the image output device 52 to the halftoning-processed image data,and outputs the data to the spooler 22, are provided in the layer ofdriver software.

[0133] Next, a particular example of image output from the applicationsoftware to the image output device 52 will be described with referenceto the flowchart of FIG. 5 showing the outline of the image processingtogether with FIG. 4.

[0134] When the application software 11 outputs an image to the imageoutput device 52, first, the application software 11 issues drawingcommands to draw character(s), line(s), figure(s), bitmap(s) and thelike, through the drawing processing interface 21 of the OS (step S1).

[0135] When the drawing commands for constructing an imageframe/printing area have been completed (step S2), the OS converts therespective drawing commands in the internal format of the OS into adevice-specific representation format (line-segmentation of respectivedrawing unit information) while calling the device-specific drawingfunctions 31-1, 31-2, . . . , 31-n inside the driver software (step S3),thereafter, delivers the image information line-segmented from the imageframe/printing area to the driver software (step S4).

[0136] Inside the driver software, the color characteristic conversionmodule 33 corrects the color characteristic of the device, and convertsthe color representation inside the driver software to that specific tothe device (step S5), further, the halftoning module 34 performsconversion (halftoning) to a quantized amounts for representingrespective pixel states of the device (step S6). Note that theconversion to quantized amount here corresponds to the form of dataprocessed by the image output device 52. If printing by the image outputdevice is performed based on e.g. binary data, binarization isperformed, and if printing by the image output device is performed basedon multivalue data (for printing by using thick/thin inks and printingby using large-sized and small-sized ink droplets), the data isN-ary-converted.

[0137] The details of the halftoning will be described in the subsequentembodiments.

[0138] The print command generation module 35 receives quantized(binarized/N-ary-converted) image data (step S7). The print commandgeneration module 35 processes the quantized image information incorrespondence with the characteristic of the image output device bydifferent methods. Further, the print command generation module 35compresses the data and adds a command header to the data (step S8).

[0139] Thereafter, the print command generation module 35 forwards thegenerated data to the spooler 22 provided in the OS (step S9), to outputthe data to the image output device 52 (step S10).

[0140] Note that in the present embodiment, the above-described controlmethod is realized by storing a program according to the flowchart ofFIG. 5 into the storage device of the host device 51 and executing theprogram.

[0141] As described above, as the core processing of the driver softwareis independent of individual image output devices, the distribution ofdata processing between the driver software and the image output devicecan be flexibly changed without impairing the construction of the driversoftware. This is advantageous in view of maintenance and management ofthe software.

[0142] Next, several embodiments using the system according to theabove-described common embodiment will be described. In the followingembodiments, the details of error diffusion processing performed by thehalftoning module 34 will be described.

[0143] Note that the error diffusion processing to be described belowhandles multivalued image data where respective pixels are representedby respectively 8-bit (256 level representation) density data of yellow(Y) component, magenta (M) component, cyan (C) component and black (K)component.

First Embodiment

[0144] In this embodiment, error diffusion processing, different fromthe error diffusion processing of the conventional art, capable ofcomplicated threshold condition processing will be described. Theprocessing handles C and M component multivalued image data.

[0145] In the present embodiment, multivalued density data is binarizedby the error diffusion processing.

[0146]FIG. 6 is a flowchart showing image formation control according tothe first embodiment of the present invention.

[0147] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0148] First, at step S10, the density values Ct and Mt of the C and Mcomponents of pixel of interest are obtained as in the case of theconventional art. Next, at step S20, a threshold value (C threshold)used in error diffusion of the C component is obtained based on theobtained M component density value Mt. More specifically, in thisembodiment, threshold tables as shown in Tables 1 and 2 are prepared inthe HDD 2002 or the DRAM 1003 of the host device 52 in advance, and thethreshold value is determined by referring to the threshold tables.

[0149] At step S30, the threshold value (C threshold) obtained at stepS20 is compared with the density value Ct of the pixel of interest. IfCt≧C threshold holds, the process proceeds to step S40, at which settingis made for printing with C ink. Thereafter, the process proceeds tostep S50. On the other hand, if Ct<C threshold holds at step S30,process skips step S40 and proceeds to step S50.

[0150] At step S50, a threshold value (M threshold) used in errordiffusion of the M component is obtained based on the obtained Ccomponent density value Ct. More specifically, in this embodiment, thethreshold tables as shown in Tables 1 and 2 are prepared in the HDD 2002or the DRAM 1003 of the host device 52 in advance, and the thresholdvalue is determined by referring to the threshold tables.

[0151] Accordingly, in this embodiment, both of the threshold tables asshown in Tables 1 and 2 are commonly used for the C component and the Mcomponent.

[0152] At step S60, the threshold value (M threshold) obtained at stepS50 is compared with the density value Mt of the pixel of interest. IfMt≧M threshold holds, the process proceeds to step S70, at which settingis made for printing with M ink. Thereafter, the process ends. On theother hand, if Mt<M threshold holds at step S60, process skips step S70and the proceeds ends.

[0153] Thus, by execution of the above processing, complicated thresholdsetting can be made only by defining threshold tables having a commonformat and setting different values in the tables, in the thresholdcondition processing as shown in FIG. 7A similar to the thresholdprocessing according to the conventional art described in FIG. 24, andfurther, in the threshold condition processing as shown in FIG. 8A withthreshold conditions more complicated than those in FIG. 7A.

[0154] Table 1 is a threshold table having threshold conditionscorresponding to FIG. 7A, and Table 2, a threshold table havingthreshold conditions corresponding to FIG. 8A. TABLE 1 THRESHOLDTHRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUEDENSITY VALUE 0 128 64 64 128 128 192 191 1 127 65 65 129 129 193 190 2126 66 66 130 130 194 189 3 125 67 67 131 131 195 188 4 124 68 68 132132 196 187 5 123 69 69 133 133 197 186 6 122 70 70 134 134 198 185 7121 71 71 135 135 199 184 8 120 72 72 136 136 200 183 9 119 73 73 137137 201 182 10 118 74 74 138 138 202 181 11 117 75 75 139 139 203 180 12116 76 76 140 140 204 179 13 115 77 77 141 141 205 178 14 114 78 78 142142 206 177 15 113 79 79 143 143 207 176 16 112 80 80 144 144 208 175 17111 81 81 145 145 209 174 18 110 82 82 146 146 210 173 19 109 83 83 147147 211 172 20 108 84 84 148 148 212 171 21 107 85 85 149 149 213 170 22106 86 86 150 150 214 169 23 105 87 87 151 151 215 168 24 104 88 88 152152 216 167 25 103 89 89 153 153 217 166 26 102 90 90 154 154 218 165 27101 91 91 155 155 219 164 28 100 92 92 156 156 220 163 29 99 93 93 157157 221 162 30 98 94 94 158 158 222 161 31 97 95 95 159 159 223 160 3296 96 96 180 160 224 159 33 95 97 97 161 161 225 168 34 94 98 98 162 162226 157 35 93 99 99 163 163 227 156 36 92 100 100 164 164 228 155 37 91101 101 165 165 229 154 38 90 102 102 168 166 230 153 39 89 103 103 167167 231 152 40 88 104 104 168 168 232 151 41 87 105 105 169 169 233 15042 86 106 106 170 170 234 149 43 85 107 107 171 171 235 148 44 84 108108 172 172 236 147 45 83 109 109 173 173 237 146 46 82 110 110 174 174238 145 47 81 111 111 175 175 239 144 48 80 112 112 176 176 240 143 4979 113 113 177 177 241 142 50 78 114 114 178 178 242 141 51 77 115 115179 179 243 140 52 76 116 116 180 180 244 139 53 75 117 117 181 181 245138 54 74 118 118 182 182 246 137 55 73 119 119 183 183 247 136 58 72120 120 184 184 248 135 57 71 121 121 185 185 249 134 58 70 122 122 186186 250 133 59 69 123 123 187 187 251 132 60 68 124 124 188 188 252 13161 67 125 125 189 189 253 130 62 66 126 126 190 190 254 129 63 65 127127 191 191 255 128

[0155] TABLE 2 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUEDENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 64 64 128 128 192 128 1127 65 65 129 128 193 128 2 126 66 66 130 128 194 128 3 125 67 67 131128 195 128 4 124 68 68 132 128 196 128 5 123 69 69 133 128 197 128 6122 70 70 134 128 198 128 7 121 71 71 135 128 199 128 8 120 72 72 136128 200 128 9 119 73 73 137 128 201 128 10 118 74 74 138 128 202 128 11117 75 75 139 128 203 128 12 116 76 76 140 128 204 128 13 115 77 77 141128 205 128 14 114 78 78 142 128 206 128 15 113 79 79 143 128 207 128 16112 80 80 144 128 208 128 17 111 81 81 145 128 209 128 18 110 82 82 146128 210 128 19 109 83 83 147 128 211 128 20 108 84 84 148 128 212 128 21107 85 85 149 128 213 128 22 106 86 86 150 128 214 128 23 105 87 87 151128 215 128 24 104- 88 88 152 128 216 128 26 103 89 89 153 128 217 12826 102 90 90 154 128 218 128 27 101 91 91 155 128 219 128 28 100 92 92156 128 220 128 29 99 93 93 157 128 221 128 30 98 94 94 158 128 222 12831 97 95 95 159 128 223 128 32 96 96 96 160 128 224 128 33 95 97 97 161128 225 128 34 94 98 98 162 128 226 128 35 93 99 99 163 128 227 128 3692 100 100 164 128 228 128 37 91 101 101 165 128 229 128 38 90 102 102166 128 230 128 39 89 103 103 167 128 231 128 40 88 104 104 188 128 232128 41 87 105 105 169 128 233 128 42 86 106 106 170 128 234 128 43 85107 107 171 128 235 128 44 84 108 108 172 128 236 128 45 83 109 109 173128 237 128 46 82 110 110 174 128 238 128 47 81 111 111 175 128 239 12848 80 112 112 176 128 240 128 49 79 113 113 177 128 241 128 50 78 114114 178 128 242 128 51 77 115 115 179 128 243 128 52 76 116 116 180 128244 128 53 75 117 117 181 128 245 128 54 74 118 118 182 128 246 128 5573 119 119 183 128 247 128 56 72 120 120 184 128 248 128 57 71 121 121185 128 249 128 58 70 122 122 186 128 250 128 59 69 123 123 187 128 251128 60 68 124 124 188 128 252 128 61 67 125 125 189 128 253 128 62 66126 126 190 128 254 128 63 65 127 127 191 128 255 128

[0156] For example, in a case where the threshold condition processingas shown in FIG. 7A is performed in accordance with the presentembodiment, first, at steps S20 to S40, the threshold conditionprocessing as shown in FIG. 7B is performed, then at steps S50 to S70,the threshold condition processing as shown in FIG. 7C is performed.

[0157] Similarly, in a case where the threshold condition processing asshown in FIG. 8A is performed in accordance with the present embodiment,first, at steps S20 to S40, the threshold condition processing as shownin FIG. 8B is performed, then at steps S50 to S70, the thresholdcondition processing as shown in FIG. 8C is performed.

[0158] Accordingly, in the above-described embodiment, as the thresholdcondition processing is performed by using a predetermined formatthreshold table, even if the threshold conditions are complicated asshown in FIGS. 9A to 9D, the processing can be performed in a simplemanner, and as the processing is simple, the complicated thresholdcondition processing can be performed at a high speed.

Second Embodiment

[0159] In the first embodiment, the multivalued density data isbinarized by the error diffusion processing; in the present embodiment,multivalued density data is ternarized by the error diffusionprocessing.

[0160]FIG. 10 is a flowchart showing the image formation controlaccording to the second embodiment of the present invention.

[0161] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0162] First, at step S100, the density values Ct and Mt of the C and Mcomponents of the pixel of interest are obtained as in the case of theconventional art. Next, at step S110, two threshold values (C threshold1and C threshold2) used in error diffusion of the C component areobtained based on the obtained M component density value Mt. Morespecifically, in this embodiment, the threshold tables as shown inTables 3 to 6 are prepared in the HDD 2002 or the DRAM 1003 of the hostdevice 52 in advance, and the threshold values are determined byreferring to the threshold tables.

[0163] At step S120, one of the threshold values (C threshold1) obtainedat step S110 is compared with the density value Ct of the pixel ofinterest. If Ct≧C threshold1 holds, the process proceeds to step S130,at which the other threshold value (C threshold2) obtained at step S110is compared with the density value Ct of the pixel of interest. If Ct≧Cthreshold2 holds, the process proceeds to step S140, at which setting ismade for printing by discharging large ink droplets using the C ink.Thereafter, the process proceeds to step S160. On the other hand, ifCt<C threshold2 holds at step S130, the process proceeds to step S150,at which setting is made for printing by discharging small ink dropletsusing the C ink. Thereafter, the process proceeds to step S160.

[0164] Further, if Ct<C threshold1 holds at step S120, the process skipssteps S130 to S150 and proceeds to step S160.

[0165] At step S160, two threshold values (M threshold1 and Mthreshold2) used in error diffusion of the M component are obtainedbased on the obtained C component density value Ct. More specifically,in this embodiment, the threshold tables as shown in Tables 3 to 6 areprepared in the HDD 2002 or the DRAM 1003 of the host device 52 inadvance, and the threshold values are determined by referring to thethreshold tables.

[0166] Accordingly, in this embodiment, the threshold tables in Tables 3to 6 are commonly used for the C component and the M component.

[0167] At step S170, one of the threshold values (M threshold1) obtainedat step S160 is compared with the density value Mt of the pixel ofinterest. If Mt≧M threshold1 holds, the process proceeds to step S180,at which the other threshold value (M threshold2) obtained at step S160is compared with the density value Mt of the pixel of interest. If Mt≧Mthreshold2 holds, the process proceeds to step S190, at which setting ismade for printing by discharging large ink droplets using the M ink.Then, the process ends. On the other hand, if Mt<M threshold2 holds atstep S180, the process proceeds to step S200, at which setting is madefor printing by discharging small ink droplets using the M ink. Then theprocess ends.

[0168] On the other hand, if Mt<M threshold1 holds at step S170, theprocess skips steps S180 to S200 and the process ends.

[0169] Thus, by execution of the above processing, complicated thresholdsetting can easily be made only by defining threshold tables having acommon format and setting different values in the tables, in thethreshold condition processing as shown in FIG. 11A, and further, in thethreshold condition processing as shown in FIG. 12A.

[0170] Tables 3 and 4 are threshold tables having threshold conditionscorresponding to FIG. 11A, and Tables 5 and 6, threshold tables havingthreshold conditions corresponding to FIG. 12A. TABLE 3 THRESHOLDTHRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITY VALUE DENSITY VALUEDENSITY VALUE 0 85 64 64 128 43 192 107 1 84 65 65 129 44 193 108 2 8366 66 130 45 194 109 3 82 67 67 131 46 195 110 4 81 68 68 132 47 196 1115 80 69 69 133 48 197 112 6 79 70 70 134 49 198 113 7 78 71 71 135 50199 114 8 77 72 72 136 51 200 115 9 76 73 73 137 52 201 116 10 75 74 74138 53 202 117 11 74 75 75 139 54 203 118 12 73 76 76 140 55 204 119 1372 77 77 141 56 205 120 14 71 78 78 142 57 206 121 15 70 79 79 143 58207 122 16 69 80 80 144 59 208 123 17 68 81 81 145 60 209 124 18 67 8282 146 61 210 125 19 66 83 83 147 62 211 126 20 65 84 84 148 63 212 12721 64 85 85 149 64 213 127 22 63 86 84 150 65 214 126 23 62 87 83 151 68215 125 24 61 88 82 152 67 216 124 25 60 89 81 153 68 217 123 26 59 9080 154 69 218 122 27 58 91 79 155 70 219 121 28 57 92 78 156 71 220 12029 56 93 77 157 72 221 119 30 55 94 76 158 73 222 118 31 54 95 75 159 74223 117 32 53 96 74 160 75 224 116 33 52 97 73 161 76 225 115 34 51 9872 162 77 226 114 35 50 99 71 163 78 227 113 36 49 100 70 164 79 228 11237 46 101 69 165 80 229 111 38 47 102 68 166 81 230 110 39 46 103 67 16782 231 109 40 45 104 66 168 83 232 108 41 44 105 65 169 84 233 107 42 43106 64 170 85 234 106 43 43 107 63 171 86 235 105 44 44 108 62 172 87236 104 45 45 109 61 173 88 237 103 46 46 110 60 174 89 236 102 47 47111 59 175 90 239 101 46 46 112 58 176 91 240 100 49 49 113 57 177 92241 99 50 50 114 56 178 93 242 98 51 51 115 55 179 94 243 97 52 52 11654 180 95 244 96 53 53 117 53 181 96 245 95 54 54 118 52 182 97 246 9455 55 119 51 183 98 247 93 56 56 120 50 184 99 246 92 57 57 121 49 185100 249 91 58 58 122 48 186 101 250 90 59 59 123 47 187 102 251 89 60 60124 46 188 103 252 88 61 61 125 45 189 104 253 87 62 62 126 44 190 105254 86 63 63 127 43 191 106 255 85

[0171] TABLE 4 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUEDENSITY VALUE DENSITY VALUE DENSITY VALUE 0 170 64 149 128 212 192 192 1169 65 150 129 211 193 193 2 168 66 151 130 210 194 194 3 167 67 152 131209 195 196 4 166 68 153 132 208 196 196 5 185 69 154 133 207 197 197 6164 70 155 134 206 198 198 7 163 71 156 135 205 199 199 8 162 72 157 136204 200 200 9 161 73 158 137 203 201 201 10 160 74 159 138 202 202 20211 159 75 160 139 201 203 203 12 158 76 161 140 200 204 204 13 157 77162 141 199 205 205 14 156 78 163 142 198 206 206 15 155 79 164 143 197207 207 16 154 80 165 144 196 208 208 17 153 81 166 145 195 209 209 18152 82 167 146 194 210 210 19 151 83 168 147 193 211 211 20 150 84 169148 192 212 212 21 149 85 170 149 191 213 212 22 148 86 171 150 190 214211 23 147 87 172 151 189 215 210 24 146 88 173 152 188 216 209 25 14589 174 153 187 217 208 26 144 90 175 154 186 218 207 27 143 91 176 155185 219 206 28 142 92 177 156 184 220 205 29 141 93 178 157 183 221 20430 140 94 179 158 182 222 203 31 139 95 180 159 181 223 202 32 138 96181 160 180 224 201 33 137 97 182 161 179 225 200 34 136 98 183 162 178226 199 35 135 99 184 163 177 227 198 36 134 100 185 164 176 228 197 37133 101 186 165 175 229 196 38 132 102 187 166 174 230 195 39 131 103188 167 173 231 194 40 130 104 189 168 172 232 193 41 129 105 190 169171 233 192 42 128 106 191 170 170 234 191 43 128 107 192 171 171 235190 44 129 108 193 172 172 236 189 45 130 109 194 173 173 237 188 46 131110 195 174 174 238 187 47 132 111 196 175 175 239 186 48 133 112 197176 176 240 185 49 134 113 198 177 177 241 184 50 135 114 199 178 178242 183 51 136 115 200 179 179 243 182 52 137 116 201 180 180 244 181 53138 117 202 181 181 245 180 54 139 118 203 182 182 246 179 55 140 119204 183 183 247 178 56 141 120 205 184 184 248 177 57 142 121 206 185185 249 176 58 143 122 207 186 186 250 175 59 144 123 208 187 187 251174 60 145 124 209 188 188 252 173 61 146 125 210 189 189 253 172 62 147126 211 190 190 254 171 63 148 127 212 191 191 255 170

[0172] TABLE 5 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUEDENSITY VALUE DENSITY VALUE DENSITY VALUE 0 85 64 64 128 85 192 85 1 8465 65 129 85 193 85 2 83 66 66 130 85 194 85 3 82 67 67 131 85 195 85 481 68 68 132 85 196 85 5 80 69 69 133 85 197 85 6 79 70 70 134 85 198 857 78 71 71 135 85 199 85 8 77 72 72 136 85 200 85 9 76 73 73 137 85 20185 10 75 74 74 138 85 202 85 11 74 75 75 139 85 203 85 12 73 76 76 14085 204 85 13 72 77 77 141 85 205 85 14 71 78 78 142 85 206 85 15 70 7979 143 85 207 85 16 69 80 80 144 85 208 85 17 68 81 81 145 85 209 85 1867 82 82 146 85 210 85 19 66 83 83 147 85 211 85 20 65 84 84 148 85 21285 21 64 85 85 149 85 213 85 22 63 86 85 150 85 214 85 23 62 87 85 15185 215 85 24 61 88 85 152 85 216 85 25 60 89 85 153 85 217 85 26 59 9085 154 85 218 85 27 58 91 85 155 85 219 85 28 57 92 85 156 85 220 85 2956 93 85 157 85 221 85 30 55 94 85 158 85 222 85 31 54 95 85 159 85 22385 32 53 96 85 160 85 224 85 33 52 97 85 161 85 225 85 34 51 98 85 16285 226 85 35 50 99 85 163 85 227 85 36 49 100 85 164 85 228 85 37 48 10185 165 85 229 85 38 47 102 85 166 85 230 85 39 46 103 85 167 85 231 8540 45 104 85 168 85 232 85 41 44 105 85 169 85 233 85 42 43 106 85 17085 234 85 43 43 107 85 171 85 235 85 44 44 108 85 172 85 236 85 45 45109 85 173 85 237 85 46 46 110 85 174 85 238 85 47 47 111 85 175 85 23985 48 48 112 85 176 85 240 85 49 49 113 85 177 85 241 85 50 50 114 85178 85 242 85 51 51 115 85 179 85 243 85 52 52 116 85 180 85 244 85 5353 117 85 181 85 245 85 54 54 118 85 182 85 246 85 55 55 119 85 183 85247 85 56 56 120 85 184 85 248 85 57 57 121 85 185 85 249 85 58 58 12285 186 85 250 85 59 59 123 85 187 85 251 85 60 60 124 85 188 85 252 8561 61 125 85 189 85 253 85 62 62 126 85 190 85 254 85 63 63 127 85 19185 255 85

[0173] TABLE 6 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUEDENSITY VALUE DENSITY VALUE DENSITY VALUE 0 170 84 170 128 170 192 170 1170 65 170 129 170 193 170 2 170 66 170 130 170 194 170 3 170 67 170 131170 195 170 4 170 68 170 132 170 196 170 5 170 69 170 133 170 197 170 6170 70 170 134 170 198 170 7 170 71 170 135 170 199 170 8 170 72 170 136170 200 170 9 170 73 170 137 170 201 170 10 170 74 170 138 170 202 17011 170 75 170 139 170 203 170 12 170 76 170 140 170 204 170 13 170 77170 141 170 205 170 14 170 78 170 142 170 206 170 15 170 79 170 143 170207 170 16 170 80 170 144 170 208 170 17 170 81 170 145 170 209 170 18170 82 170 146 170 210 170 19 170 83 170 147 170 211 170 20 170 84 170148 170 212 170 21 170 85 170 149 170 213 170 22 170 86 170 150 170 214170 23 170 87 170 151 170 215 170 24 170 88 170 152 170 216 170 25 17089 170 153 170 217 170 26 170 90 170 154 170 218 170 27 170 91 170 155170 219 170 28 170 92 170 156 170 220 170 29 170 93 170 157 170 221 17030 170 94 170 158 170 222 170 31 170 95 170 159 170 223 170 32 170 96170 160 170 224 170 33 170 97 170 161 170 225 170 34 170 98 170 162 170226 170 35 170 99 170 163 170 227 170 36 170 100 170 164 170 228 170 37170 101 170 165 170 229 170 38 170 102 170 166 170 230 170 39 170 103170 167 170 231 170 40 170 104 170 168 170 232 170 41 170 105 170 169170 233 170 42 170 106 170 170 170 234 170 43 170 107 170 171 170 235170 44 170 108 170 172 170 236 170 45 170 109 170 173 170 237 170 46 170110 170 174 170 238 170 47 170 111 170 175 170 239 170 48 170 112 170176 170 240 170 49 170 113 170 177 170 241 170 50 170 114 170 178 170242 170 51 170 115 170 179 170 243 170 52 170 116 170 180 170 244 170 53170 117 170 181 170 245 170 54 170 118 170 182 170 246 170 55 170 119170 183 170 247 170 56 170 120 170 184 170 248 170 57 170 121 170 185170 249 170 58 170 122 170 186 170 250 170 59 170 123 170 187 170 251170 60 170 124 170 188 170 252 170 61 170 125 170 189 170 253 170 62 170126 170 190 170 254 170 63 170 127 170 191 170 255 170

[0174] For example, in a case where the threshold condition processingas shown in FIG. 11A is performed in accordance with the presentembodiment, first, at steps S110 to S150, the threshold conditionprocessing as shown in FIG. 11B is performed, then at steps S160 toS200, the threshold condition processing as shown in FIG. 11C isperformed.

[0175] Similarly, in a case where the threshold condition processing asshown in FIG. 12A is performed in accordance with the presentembodiment, first, at steps S110 to S150, the threshold conditionprocessing as shown in FIG. 12B is performed, then at steps S160 toS200, the threshold condition processing as shown in FIG. 12C isperformed. Especially, the threshold conditions shown in FIGS. 12A to12C are effective for improvement in uniformity of halftone image.

[0176] Accordingly, in the above-described embodiment, even internarization of multivalued image data, as the threshold conditionprocessing is performed by using a predetermined format threshold table,even if the threshold conditions are complicated, the processing can beperformed in a simple manner, and as the processing is simple, thecomplicated threshold condition processing can be performed at a highspeed.

[0177] Note that in the present embodiment, only ternarization ishandled, however, if the ink-jet printer as the image output device iscapable of handling quaternary or quinary representation by using dropmodulation and same-color various density ink (e.g. thin cyan ink, thickcyan ink, thin magenta ink and thick magenta ink), threshold tables formultivalue error diffusion processing such as quaternarization orquinarization may be generated.

Third Embodiment

[0178] In the first and second embodiments, the C and M components amongthe multivalued density data are handled; in the present embodiment, theK component in addition to these components is handled.

[0179]FIG. 13 is a flowchart showing the image formation controlaccording to the third embodiment of the present invention.

[0180] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0181] First, at step S210, the density values Ct, Mt and Kt of the C, Mand K components of pixel of interest are obtained. Next, at step S220,a threshold value (C threshold) used in error diffusion of the Ccomponent is obtained based on the obtained M and K component densityvalues Mt and Kt. More specifically, in this embodiment, a thresholdtable as shown in Table 7 is prepared in the HDD 2002 or the DRAM 1003of the host device 52 in advance, and the threshold value is determinedby referring to the threshold table.

[0182] At step S230, the threshold value (C threshold) obtained at stepS220 is compared with the density value Ct of the pixel of interest. IfCt≧C threshold holds, the process proceeds to step S240, at whichsetting is made for printing with the C ink. Thereafter, the processproceeds to step S250. On the other hand, if Ct<C threshold holds atstep S230, process skips step S240 and proceeds to step S250.

[0183] At step S250, a threshold value (M threshold) used in errordiffusion of the M component is obtained based on the obtained C and Kcomponent density values Ct and Kt. More specifically, in thisembodiment, a threshold table as shown in Table 7 is prepared in the HDD2002 or the DRAM 1003 of the host device 52 in advance, and thethreshold value is determined by referring to the threshold table.

[0184] At step S260, the threshold value (M threshold) obtained at stepS250 is compared with the density value Mt of the pixel of interest. IfMt≧M threshold holds, the process proceeds to step S270, at whichsetting is made for printing with the M ink. Thereafter, the processproceeds to step S280. On the other hand, if Mt<M threshold holds atstep S260, the process skips step S270 and proceeds to step S280.

[0185] Further, at step S280, a threshold value (K threshold) used inerror diffusion of the K component is obtained based on the obtained Cand M component density values Ct and Mt. More specifically, in thisembodiment, a threshold table as shown in Table 7 is prepared in the HDD2002 or the DRAM 1003 of the host device 52 in advance, and thethreshold value is determined by referring to the threshold table.

[0186] Accordingly, in this embodiment, the threshold table in Table 7is commonly used for the C component, the M component and the Kcomponent.

[0187] At step S290, the threshold value (K threshold) obtained at stepS280 is compared with the density value Kt of the pixel of interest. IfKt≧K threshold holds, the process proceeds to step S300, at whichsetting is made for printing with K ink. Then, the process ends. On theother hand, if Kt<K threshold holds, the process skips step S300 and theprocess ends.

[0188] The code representing the core part of the above processing is asfollows. Ct=C+Cerr Mt=M+Merr Kt=K+Kerr Cthreshold=C₋Threshold₋Table[Mt+Kt] If (Ct>=Cthreshold) Print C Mthreshold=M₋Threshold₋Table [Ct+Kt]If (Mt>=Mthreshold) Print M Kthreshold=M₋Threshold₋Table [Ct+Mt] If(Kt>=Kthreshold) Print K

[0189] By executing the above processing, the threshold conditionprocessing for three components, which is complicated in theconventional art as explained by using program code, can easily beperformed only by defining a threshold table having a common format andsetting different values in the threshold table.

[0190] Table 7 is a threshold table commonly used for the C, M and Kcomponents. TABLE 7 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITYVALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 84 64 128 128 192128 1 127 65 65 129 128 193 128 2 126 66 66 130 128 194 128 3 125 67 67131 128 195 128 4 124 68 68 132 128 196 128 5 123 69 69 133 128 197 1286 122 70 70 134 128 198 128 7 121 71 71 135 128 199 128 8 120 72 72 136128 200 128 9 119 73 73 137 128 201 128 10 118 74 74 138 128 202 128 11117 75 75 139 128 203 128 12 116 76 76 140 128 204 128 13 115 77 77 141128 205 128 14 114 78 78 142 128 206 128 15 113 79 79 143 128 207 128 16112 80 80 144 128 208 128 17 111 81 81 145 128 209 128 18 110 82 82 146128 210 128 19 109 83 83 147 128 211 128 20 108 84 84 148 128 212 128 21107 85 85 149 128 213 128 22 106 86 86 150 128 214 128 23 105 87 87 151128 215 128 24 104 88 88 152 128 216 128 25 103 89 89 153 128 217 128 26102 90 90 154 128 218 128 27 101 91 91 155 128 219 128 28 100 92 92 156128 220 128 29 99 93 93 157 128 221 128 30 98 94 94 158 128 222 128 3197 95 95 159 128 223 128 32 96 96 96 160 128 224 128 33 95 97 97 161 128225 128 34 94 98 98 162 128 226 128 35 93 99 99 163 128 227 128 36 92100 100 164 128 228 128 37 91 101 101 165 128 229 128 38 90 102 102 166128 230 128 39 89 103 103 167 128 231 128 40 88 104 104 168 128 232 12841 87 105 105 169 128 233 128 42 86 106 106 170 128 234 128 43 85 107107 171 128 235 128 44 84 108 108 172 128 236 128 45 83 109 109 173 128237 128 46 82 110 110 174 128 238 128 47 81 111 111 175 128 239 128 4880 112 112 176 128 240 128 49 79 113 113 177 128 241 128 50 78 114 114178 128 242 128 51 77 115 115 179 128 243 128 52 76 116 116 180 128 244128 53 75 117 117 181 128 245 128 54 74 118 118 182 128 246 128 55 73119 119 183 128 247 128 56 72 120 120 184 128 248 128 57 71 121 121 185128 249 128 58 70 122 122 188 128 250 128 59 69 123 123 187 128 251 12860 68 124 124 188 128 252 128 61 67 125 125 189 128 253 128 62 66 126126 190 128 254 128 63 65 127 127 191 128 255 128

[0191] Accordingly, in the above-described embodiment, as the thresholdconditional processing is performed by using a predetermined formatthreshold table, even the error diffusion processing handling threecomponents with complicated threshold conditions can be performed in asimple manner, and as the processing is simple, the complicatedthreshold condition processing can be performed at a high speed.

[0192] Further, if the present embodiment is combined with theternarization processing of the second embodiment, the advantages ofsimplification and increase in processing speed can be further improved.

[0193] Note that the present invention is not limited to the thresholdtables described in the above-described embodiments. If the format ofthe threshold table is maintained while the values set in the table arechanged, processing can be performed with various threshold conditionsas follows.

[0194] (1) instead of the sum of the C and M component density values(C+M), threshold conditions such as the sum of squares of the C and Mcomponent density values (C²+M²) are employed. Table 8 is a thresholdtable used in this case. TABLE 8 THRESHOLD THRESHOLD THRESHOLD THRESHOLDDENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 128 64 110 128128 192 143 1 127 65 110 129 129 193 143 2 127 66 109 130 130 194 142 3127 67 109 131 131 195 141 4 127 68 108 132 132 196 141 5 127 69 107 133133 197 140 6 127 70 107 134 134 198 140 7 127 71 106 135 135 199 139 8127 72 105 136 136 200 139 9 127 73 105 137 137 201 138 10 127 74 104138 138 202 138 11 127 75 103 139 139 203 138 12 127 76 102 140 140 204137 13 127 77 102 141 141 205 137 14 127 78 101 142 142 206 136 15 12779 100 143 143 207 138 16 126 80 99 144 144 208 135 17 126 81 99 145 145209 135 18 126 82 98 146 146 210 135 19 126 83 97 147 147 211 134 20 12684 96 148 148 212 134 21 126 85 95 149 149 213 134 22 126 86 94 150 150214 133 23 125 87 93 151 151 215 133 24 125 88 92 152 152 216 133 25 12589 91 153 153 217 132 26 125 90 91 154 154 218 132 27 125 91 91 155 155219 132 28 124 92 92 156 156 220 131 29 124 93 93 157 157 221 131 30 12494 94 158 158 222 131 31 124 95 95 159 159 223 131 32 123 96 96 160 160224 130 33 123 97 97 161 161 225 130 34 123 98 98 162 162 226 130 35 12399 99 163 163 227 130 36 122 100 100 164 164 228 129 37 122 101 101 165163 229 129 38 122 102 102 166 163 230 129 39 121 103 103 167 162 231129 40 121 104 104 168 161 232 129 41 121 105 105 169 160 233 128 42 120106 106 170 159 234 128 43 120 107 107 171 158 235 128 44 120 108 108172 157 236 128 45 119 109 109 173 156 237 128 46 119 110 110 174 155238 128 47 119 111 111 175 155 239 128 48 118 112 112 176 154 240 127 49118 113 113 177 153 241 127 50 117 114 114 178 152 242 127 51 117 115115 179 152 243 127 52 116 116 116 180 151 244 127 53 116 117 117 181150 245 127 54 116 118 118 182 149 246 127 55 115 119 119 183 149 247127 56 115 120 120 184 148 248 127 57 114 121 121 185 147 249 127 58 114122 122 186 147 250 127 59 113 123 123 187 146 251 127 60 113 124 124188 145 252 127 61 112 125 125 189 145 253 127 62 111 126 126 190 144254 127 63 111 127 127 191 144 255 127

[0195] In a case where an ink-jet printer having a slightly greater inkdischarge amount is used as the image output device, isolated dotsformed by the C or M ink are easily recognized in a very low densityimage area, and the uniformity of the image is impaired by exclusivearrangement of these dots, if the above threshold conditions are used,the correlation between the C component and the M component can beslightly lowered and the uniformity of the image can be maintained.

[0196] (2) As shown in FIG. 9B, threshold conditions overlapped withnoise are employed. Table 9 is a threshold table used in this case.TABLE 9 THRESHOLD THRESHOLD THRESHOLD THRESHOLD DENSITY VALUE DENSITYVALUE DENSITY VALUE DENSITY VALUE 0 130 64 66 128 130 192 193 1 127 6565 129 129 193 190 2 124 66 64 130 128 194 187 3 125 67 67 131 131 195188 4 126 68 70 132 134 196 189 5 123 69 69 133 133 197 186 6 120 70 68134 132 198 183 7 121 71 71 135 135 199 184 8 122 72 74 136 138 200 1859 119 73 73 137 137 201 182 10 116 74 72 138 136 202 179 11 117 75 75139 139 203 180 12 116 76 78 140 142 204 181 13 115 77 77 141 141 205178 14 112 78 76 142 140 206 175 15 113 79 79 143 143 207 176 16 114 8082 144 148 208 177 17 111 81 81 145 145 209 174 18 108 82 80 146 144 210171 19 109 83 83 147 147 211 172 20 110 84 86 148 150 212 173 21 107 8585 149 149 213 170 22 104 86 84 150 148 214 167 23 105 87 87 151 151 215168 24 106 88 90 152 154 216 169 25 103 89 89 153 153 217 166 26 100 9088 154 152 218 163 27 101 91 91 155 155 219 164 28 102 92 94 156 158 220165 29 99 93 93 157 157 221 162 30 96 94 92 158 156 222 159 31 97 95 95159 159 223 160 32 98 96 98 160 162 224 161 33 95 97 97 161 161 225 15834 92 98 96 162 160 226 155 35 93 99 99 163 163 227 156 36 94 100 102164 166 228 157 37 91 101 101 165 165 229 154 38 88 102 100 166 164 230151 39 89 103 103 167 167 231 152 40 90 104 106 168 170 232 153 41 87105 105 169 169 233 150 42 84 106 104 170 168 234 147 43 85 107 107 171171 235 148 44 86 108 110 172 174 236 149 45 83 109 109 173 173 237 14646 80 110 108 174 172 238 143 47 81 111 111 175 175 239 144 48 82 112114 176 178 240 145 49 79 113 113 177 177 241 142 50 76 114 112 178 176242 139 51 77 115 115 179 179 243 140 52 78 116 118 180 182 244 141 5375 117 117 181 181 245 138 54 72 118 116 182 180 246 135 55 73 119 119183 183 247 136 56 74 120 122 184 186 248 137 57 71 121 121 185 185 249134 58 68 122 120 186 184 250 131 59 69 123 123 187 187 251 132 60 70124 126 188 190 252 133 61 67 125 125 189 189 253 130 62 64 126 124 190188 254 127 63 65 127 127 191 191 255 128

[0197] By using the threshold conditions, the probability of formationof continuous C-ink or M-ink dots can be reduced.

[0198] (3) As shown in FIG. 9C, the tendency of error diffusion ischanged in a highlight area and intermediate to high density areas. Byusing the threshold conditions, the degradation of image quality due tofluctuation of ink dot application position can be reduced.

[0199] (4) As shown in FIG. 9D, the boundaries of thresholds aresmoothed as much as possible. By using such threshold conditions, theabrupt change can be reduced between an area where C and N inks areexclusively used and an area where the C and M inks are not exclusivelyused, and capability of representing an image can be improved.

[0200] In this manner, the threshold condition processing hasflexibility by use of a threshold table. If the threshold table is usedin combination with actual ink discharge amount or ink composition inthe ink-jet printer, the content of image formation processing and/orpurpose of the processing can be easily changed.

Fourth Embodiment

[0201] Further, assume that the ink-jet printer IJRA can handlemultivalued image data by using drop modulation and/or same-color thickand thin inks (e.g., thin cyan ink, thick cyan ink, thin magenta ink andthick magenta ink).

[0202] In the present embodiment, unlike the conventional art,multivalued density data is ternarized by the error diffusionprocessing. The data handled by the error diffusion processing accordingto this embodiment is C component and M component multivalued imagedata.

[0203]FIG. 14 is a flowchart showing the image formation controlaccording to the fourth embodiment of the present invention.

[0204] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0205] First, at step S310, the density values Ct and Mt of the C and Mcomponents of pixel of interest are obtained as in the case of theconventional art. Next, at step S320, it is determined whether or notthe sum of the obtained M component density value Mt and the C componentdensity value Ct is greater than a first threshold value (Threshold1).If Ct+Mt>Threshold1 holds, the process proceeds to step S330, at whichit is determined whether or not the sum of the M component density valueMt and the C component density value Ct is less than a second thresholdvalue (Threshold2). On the other hand, if Ct+Mt<Threshold1 holds at stepS320, the process ends.

[0206] At step S330, if Ct+Mt<Threshold2 holds, the process proceeds tostep S340, at which the M component density value Mt and the C componentdensity value Ct are compared with each other. If Ct>Mt holds, theprocess proceeds to step S350, at which setting is made for printingwith small-sized C ink droplet (or thin C ink). On the other hand, ifCt≦Mt holds, the process proceeds to step S360, at which setting is madefor printing with small-sized M ink droplet (or thin M ink). After stepS350 or S360, the process ends.

[0207] At step S330, if Ct+Mt≧Threshold2 holds, the process proceeds tostep S370, at which it is determined whether or not the sum of the Mcomponent density value Mt and the C component density value Ct is lessthan a third threshold value (Threshold3). If Ct+Mt<Threshold3 holds,the process proceeds to step S380, at which it is determined whether ornot the difference between the M component density value Mt and the Ccomponent density value Ct is greater than a predetermined offset value(Offset1). If Ct−Mt>Offset1 holds, the process proceeds to step S390, atwhich setting is made for printing with large-sized C ink droplet (orthick C ink). Then, the process ends. On the other hand, ifCt−Mt≦Offset1 holds, the process proceeds to step S400.

[0208] At step S400, it is determined whether or not the differencebetween the M component density value Mt and the C component densityvalue Ct is greater than a predetermined offset value (Offset2). IfMt−Ct≦Offset2 holds, the process proceeds to step S410, at which settingis made for printing with small-sized C ink droplet (or thin C ink) andsmall-sized M ink droplet (or thin M ink). Then, the process ends. Onthe other hand, if Mt−Ct>Offset2 holds, the process proceeds to stepS420, at which setting is made for printing with large-sized M inkdroplet (or thick M ink). Then, the process ends.

[0209] Further, at step S370, if Ct+Mt≧Threshold3 holds, the processproceeds to step S430, at which it is determined whether or not the sumof the M component density value Mt and the C component density value Ctis less than a fourth threshold value (Threshold4). If Ct+Mt<Threshold4holds, the process proceeds to step S440, at which the M componentdensity value Mt and the C component density value Ct are compared witheach other. If Ct>Mt holds, the process proceeds to step S450, at whichsetting is made for printing with large-sized C ink droplet (or thick Cink) and small-sized M ink droplet (or thin M ink). Then the processends. On the other hand, if Ct≦Mt holds, the process proceeds to stepS460, at which setting is made for printing with small-sized C inkdroplet (or thin C ink) and large-sized M ink droplet (or thick M ink).Then, the process ends.

[0210] On the other hand, at step S430, if Ct+Mt≧Threshold4 holds, theprocess proceeds to step S470, at which setting is made for printingwith large-sized C ink droplet (or thick C ink) and large-sized M inkdroplet (or thick M ink). Then, the process ends.

[0211]FIG. 15 shows the threshold conditions for the C and M componentsin the processing shown in FIG. 14.

[0212] In the above-described processing, the following dot arrangementsare made in accordance with the M component density value Mt and the Ccomponent density value Ct.

[0213] (1) Ct+Mt≦Threshold1

[0214] (C and M components belong to low density area→area (a) in FIG.15)

[0215] Dot printing is not performed.

[0216] (2) Ct+Mt>Threshold1 and Ct+Mt<Threshold2 and Ct>Mt

[0217] (C component belongs to intermediate density area→area (b) inFIG. 15)

[0218] Dot printing with small-sized C ink droplet (or thin Cink)(exclusive printing).

[0219] (3) Ct+Mt>Threshold1 and Ct+Mt<Threshold2 and Ct≦Mt

[0220] (M component belongs to intermediate density area→area (c) inFIG. 15)

[0221] Dot printing with small-sized M ink droplet (or thin Mink)(exclusive printing).

[0222] (4) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3and Ct−Mt>Offset1

[0223] (C component belongs to high density area→area (d) in FIG. 15)

[0224] Dot printing with large-sized C ink droplet (or thick Cink)(exclusive printing).

[0225] (5) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3and Ct−Mt≦Offset1 and Mt−Ct≦Offset2

[0226] (C and M components belong to intermediate density area→area (e)in FIG. 15)

[0227] Dot printing with small-sized C ink droplet (or thin C ink) andsmall-sized M ink droplet (or thin M ink) (overlay printing).

[0228] (6) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt<Threshold3and Mt−Ct≦Offset1 and Mt−Ct>Offset2

[0229] (M component belongs to high density area→area (f) in FIG. 15)

[0230] Dot printing with large-sized M ink droplet (or thick M ink)(exclusive printing).

[0231] (7) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt≧Threshold3and Ct+Mt<Threshold4 and Ct>Mt

[0232] (C component belongs to high density area and M component belongsto intermediate density area→area (g) in FIG. 15)

[0233] Dot printing with large-sized C ink droplet (or thick C ink) andsmall-sized M ink droplet (or thin M ink)(overlay printing).

[0234] (8) Ct+Mt>Threshold1 and Ct+Mt≧Threshold2 and Ct+Mt≧Threshold3and Ct+Mt<Threshold4 and Ct≦Mt

[0235] (C component belongs to intermediate density area and M componentbelongs to high density area→area (h) in FIG. 15)

[0236] Dot printing with small-sized C ink droplet (or thin C ink) andlarge-sized M ink droplet (or thick M ink) (overlay printing).

[0237] (9) Ct+Mt≧Threshold4 (>Threshold3>Threshold2>Threshold1)

[0238] (C and M components belong to high density area→area (i) in FIG.15)

[0239] Dot printing with large-sized C ink droplet (or thick C ink) andlarge-sized M ink droplet (or thick M ink) (overlay printing).

[0240] Accordingly, in the above-described present embodiment, as theprinting with the M ink and C ink is changed in accordance with the Ccomponent and M component density values, printing with reducedgraininess can be performed by ternarizing the C component and Mcomponent density values and exclusively arranging printed dots based onthe ternarization.

Fifth Embodiment

[0241] In the fourth embodiment, the multivalued density data isternarized by the error diffusion processing; in the present embodiment,an example of high-speed processing in consideration of conversion ofmultivalued density data into N-ary code (N≧4) by the error diffusionwill be described.

[0242] As it is apparent from the flowchart of FIG. 14 described in thefirst embodiment, in the case of ternarization, the C and M componentsare respectively ternarized, 9 (=3×3) arrangements are considered andbranching processings by 8 “if” statements (condition statements) arerequired. That is, in the case of converting into N-ary code, N²−1 “if”statements are required. Accordingly, as the value of N increases,processing time increases.

[0243]FIG. 16 is a flowchart showing the image formation controlaccording to the fifth embodiment of the present invention.

[0244] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0245] In the present embodiment, as the threshold condition processingis very complicated in the conversion of input multivalued image datainto N-ary code (N≧3) by the error diffusion processing, the conversionis made by the following procedure.

[0246] (1) Functions defined as X=Ct+Mt and Y=Ct−Mt are introduced forexecution of multivalue error diffusion.

[0247] (2) A two-dimensional table is referred to based on the result ofmultivalue error diffusion processing, so as to determine arrangement ofdots to be printed and dot type. The two-dimensional table may be acommon table for the C and M components, however, actually, it ispreferable that tables (C_Table and M_Table) respectively for the C andM components are prepared.

[0248] Returning to FIG. 16, first, at step S510, X and Y values aredetermined from density values of the C and M components in each pixel.

[0249] Next, at step S520, arguments (X_index, Y_index) of theabove-described two-dimensional table are determined based on the X andY values. In this embodiment, the arguments are determined as X and Yfunctions (X_index=f(X), Y_index=g(Y)).

[0250] Finally, at step S530, the two-dimensional table is referred toby using the arguments determined at step S520, and output values by theerror diffusion processing of the C and M components (C out, M out) aredetermined.

[0251] For comparison, an example of ternarization processing the sameas that described in the fourth embodiment, in accordance with thepresent embodiment, will be described.

[0252]FIG. 17 shows the ternarization according to the fifth embodiment.

[0253]FIG. 17 shows quaternarization of X=Ct(=C+Cerr)+Mt(=M+Merr) andquinarization of Y=Ct(=C+Cerr)−Mt(=M+Merr).

[0254] In FIG. 17, a right-upward straight line indicates the same Xvalue (=Ct−Mt), and a left-upward straight line, the same Y value(=Ct+Mt) (Ct and Mt have variation widths of about −128≦Ct, Mt≦383including error-accumulation).

[0255] Accordingly, as the values Ct and Mt have the above variationwidths, the X value has a variation width of about −256≦X≦766, and the Yvalue, a variation width of about −511≦Y≦511. To quaternarize andquinarize the X and Y values having the above variation widths, thefunction of X (f(X)) and that of Y (g(Y)) are introduced.

[0256] That is, X_index=f(X) and Y_index=g(Y) are calculated. Thecalculations can be realized by referring to the table.

[0257] In this manner, two additions and two multivalue conversioncalculations (referring to the table) divide the entire X and Y rangeinto quaternary×quinary=20 sections.

[0258] In comparison between FIGS. 17 and 15, the areas (a), (b), (c),(e), (g), (h) and (i) in FIG. 15 are respectively 2 sections in FIG. 17.The entire partitioning is approximately common to FIGS. 15 and 17.

[0259] Accordingly, print control based on the error-diffusionprocessing by C and M ternarization can be performed by referring to acommon two-dimensional table as shown in FIG. 18 based on the results ofX and Y multivalue conversion.

[0260] Note that in FIG. 18, “_” means non-execution of dot printingwith C or M ink; “c”, dot printing with small-sized C ink droplet (orthin C ink); “m”, dot printing with small-sized M ink droplet (or thin Mink); “C”, dot printing with large-sized C ink droplet (or thick C ink);“M”, dot printing with large-sized M ink droplet (or thick M ink); “cm”,dot printing with small-sized C ink droplet (or thin C ink) andsmall-sized M ink droplet (or thin M ink); “Cm”, dot printing withlarge-sized C ink droplet (or thick C ink) and small-sized M ink droplet(or thin M ink); “cM”, dot printing with small-sized C ink droplet (orthin C ink) and large-sized M ink droplet (or thick M ink); and “CM”,dot printing with large-sized C ink droplet (or thick C ink) andlarge-sized M ink droplet (or thick M ink).

[0261] Actually, it is desirable that two-dimensional tables areprepared respectively for the C and M components in consideration ofcolor characteristics of the C and M components, as shown in FIGS. 19Aand 19B.

[0262]FIG. 19A shows a two-dimensional table specialized for the Ccomponent, and FIG. 19B, a two-dimensional table specialized for the Mcomponent.

[0263] Further, in FIGS. 19A and B, “_” means non-execution of dotprinting; “c”, dot printing with small-sized C ink droplet (or thin Cink); “m”, dot printing with small-sized M ink droplet (or thin M ink);“C”, dot printing with large-sized C ink droplet (or thick C ink); and“M”, dot printing with large-sized M ink droplet (or thick M ink).

[0264] In the above example, for the sake of simplification ofexplanation, ternarization has been described, however, in the presentembodiment, as conversion into N-ary code (N≧4) can be realized by usingsimple processing steps without conditional branch processing, i.e., XYcalculation, XY multivalue conversion processing and multivalueconversion of the C and M components, the embodiment provides moreeffective processing for N of the higher-order.

[0265] Accordingly, in the above-described present embodiment, regardingconversion into N-ary code of the higher-order, the error diffusionprocessing can be performed at a high speed without complicatedprocessing.

[0266] Further, according to the above-described present embodiment, asthe processing is mainly performed with reference to table(s) withoutcalculation accompanied with condition determination, the processing isadvantageous in e.g. pipeline processing and/or lookahead processingused in an MPU such as an Pentium compatible processor. If suchprocessor is employed in the present embodiment, higher-speed processingcan be expected.

Sixth Embodiment

[0267] In the present embodiment, the error diffusion processing capableof controlling pixel arrangement by each density component in accordancewith density value, different from the error diffusion of theconventional art, will be described. The error diffusion processingaccording to the present embodiment handles multivalued image data of Cand M components.

[0268] In the present embodiment, the multivalued density data isbinarized by the error-diffusion processing.

[0269]FIG. 20 is a flowchart showing the image formation controlaccording to the sixth embodiment of the present invention.

[0270] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0271] First, at step S610, the density values Ct and Mt of the C and Mcomponents of pixel of interest are obtained as in the case of theconventional art. Next, at step S620, it is determined whether or notthe sum of the obtained M component density value Mt and the C componentdensity value Ct is greater than a density value 127 used as a thresholdvalue. If Ct+Mt>127 holds, the process proceeds to step S630, at whichthe M component density value Mt and the C component density value Ctare compared with each other.

[0272] If Ct>Mt holds, the process proceeds to step S640, at whichsetting is made for printing with the C ink. Further, at step S650, itis determined whether or not the M component density value Mt is greaterthan the threshold value 127. If Mt>127 holds, the process proceeds tostep S670, at which setting is made for printing with the M ink. Thenthe process ends. On the other hand, if Mt≦127 holds, the process skipsstep S670 and the process ends.

[0273] At step S630, if Ct≦Mt holds, the process proceeds to step S680,at which setting is made for printing with the M ink. Further, theprocess proceeds to step S690, at which it is determined whether or notthe C component density value Ct is greater than the threshold value127. If Ct>127 holds, the process proceeds to step S700, at whichsetting is made for printing with the C ink. Then, the process ends. Onthe other hand, if Ct≦127 holds, the process skips step S700 and theprocess ends.

[0274] Further, at step S620, if Ct+Mt≦127 holds, the process ends.

[0275]FIG. 21 is a diagram showing threshold conditions for the C and Mcomponents in the processing shown in FIG. 20.

[0276] In the above-described processing, the following dot arrangementsare made in accordance with the M component density value Mt and the Ccomponent density value Ct.

[0277] (1) Ct+Mt≦127

[0278] (C and M components belong to low density area→area (a) in FIG.21)

[0279] Dot printing is not performed.

[0280] (2) Ct+Mt>127 and Ct>Mt and Mt>127

[0281] (C and M components belong to intermediate to high densityarea→area (d) in FIG. 21)

[0282] Dot printing with C and M inks (overlay printing).

[0283] (3) Ct+Mt>127 and Ct>Mt and Mt≦127

[0284] (only C component belongs to intermediate to high densityarea→area (b) in FIG. 21)

[0285] Dot printing with only C ink (exclusive printing).

[0286] (4) Ct+Mt>127 and Ct<Mt and Ct>127

[0287] (C and M components belong to intermediate to high densityarea→area (d) in FIG. 21)

[0288] Dot printing with C and M inks (overlay printing).

[0289] (5) Ct+Mt>127 and Ct≦Mt and Ct≦127

[0290] (only M component belongs to intermediate to high densityarea→area (c) in FIG. 21)

[0291] Dot printing with only M ink (exclusive printing).

[0292] Accordingly, in the above-described embodiment, if only onedensity component has a sufficiently high density, printing pixels areformed for the color component without depending on another component.Thus, printing independency of the C and M components in intermediate tohigh density areas is enhanced. Thus the uniformity of image can bemaintained in intermediate and higher density areas.

Seventh Embodiment

[0293] In the sixth embodiment, the multivalued density data isbinarized by the error diffusion processing; in the present embodiment,multivalued density data is ternarized by the error diffusionprocessing.

[0294]FIG. 22 is a flowchart showing the image formation controlaccording to the seventh embodiment of the present invention.

[0295] Hereinbelow, the feature of the present embodiment will bedescribed with reference to the flowchart.

[0296] First, at step S710, the density values Ct and Mt of the C and Mcomponents of pixel of interest are obtained as in the case of theconventional art. Next, at step S720, the sum of the obtained Mcomponent density value Mt and the C component density value Ct iscompared with a threshold value (Threshold). If Ct+Mt>Threshold holds,the process proceeds to step S730, while if Ct+Mt≦Threshold holds,proceeds to step S760.

[0297] At step S730, the M component density value Mt and the Ccomponent density value Ct are compared with each other. If Ct>Mt holds,the process proceeds to step S740, at which output values by the errordiffusion processing of the C and M components are determined.

[0298] That is, a common multivalue conversion table for the C and Mcomponents as shown in Table 10 is used. First, as the C componentoutput value (C out), a greater one of “1” and f(Ct) value (inmultivalue conversion table as a function of a density value Ct) isselected. For example, if f(Ct) is “0”, C out=1 holds; if f(Ct) is “1”,C out=1 holds; and if f(Ct) is “2”, C out=2 holds.

[0299] Further, as the M component output value (M out), a valuecorresponding to the density value Mt is determined by referring to themultivalue conversion table of Table 10, as M out=g(Mt)(in multivalueconversion table as a function of a density value Mt). TABLE 10MULTIVALUE MULTIVALUE MULTIVALUE MULTIVALUE OUTPUT OUTPUT OUTPUT OUTPUTDENSITY VALUE DENSITY VALUE DENSITY VALUE DENSITY VALUE 0 0 64 0 128 1192 2 1 0 65 0 129 1 193 2 2 0 66 0 130 1 194 2 3 0 67 0 131 1 195 2 4 068 0 132 1 196 2 5 0 69 0 133 1 197 2 6 0 70 0 134 1 198 2 7 0 71 0 1351 199 2 8 0 72 0 136 1 200 2 9 0 73 0 137 1 201 2 10 0 74 0 138 1 202 211 0 75 0 139 1 203 2 12 0 76 0 140 1 204 2 13 0 77 0 141 1 205 2 14 078 0 142 1 206 2 15 0 79 0 143 1 207 2 16 0 80 0 144 1 208 2 17 0 81 0145 1 209 2 18 0 82 0 146 1 210 2 19 0 83 0 147 1 211 2 20 0 84 0 148 1212 2 21 0 85 1 149 1 213 2 22 0 86 1 150 1 214 2 23 0 87 1 151 1 215 224 0 88 1 152 1 216 2 25 0 89 1 153 1 217 2 26 0 90 1 154 1 218 2 27 091 1 155 1 219 2 28 0 92 1 156 1 220 2 29 0 93 1 157 1 221 2 30 0 94 1158 1 222 2 31 0 95 1 159 1 223 2 32 0 96 1 160 1 224 2 33 0 97 1 161 1225 2 34 0 98 1 162 1 226 2 35 0 99 1 163 1 227 2 36 0 100 1 164 1 228 237 1 101 1 165 1 229 2 38 0 102 1 166 1 230 2 39 0 103 1 167 1 231 2 400 104 1 168 1 232 2 41 0 105 1 169 1 233 2 42 0 106 1 170 2 234 2 43 0107 1 171 2 235 2 44 0 108 1 172 2 236 2 45 0 109 1 173 2 237 2 46 0 1101 174 2 238 2 47 0 111 1 175 2 239 2 48 0 112 1 176 2 240 2 49 0 113 1177 2 241 2 50 0 114 1 178 2 242 2 51 0 115 1 179 2 243 2 52 0 116 1 1802 244 2 53 0 117 1 181 2 245 2 54 0 118 1 182 2 246 2 55 0 119 1 183 2247 2 56 0 120 1 184 2 248 2 57 0 121 1 185 2 249 2 58 0 122 1 186 2 2502 59 0 123 1 187 2 251 2 60 0 124 1 188 2 252 2 61 0 125 1 189 2 253 262 0 126 1 190 2 254 2 63 0 127 1 191 2 255 2

[0300] Further, if Ct≦Mt holds, the process proceeds to step S750, atwhich the common multivalue conversion table for the C and M componentsshown in the Table 10 is referred to, and the output values from theerror diffusion processing of the C and M components are determined.

[0301] That is, as the C component output value (C out), a valuecorresponding to the density value Ct is determined by referring to themultivalue conversion table of Table 10, as C out=f(Ct), and as the Mcomponent output value (M out), a greater one of “1” and g(Mt) value (inmultivalue conversion table as a function of a density value Mt) isselected.

[0302] Further, at step S760, the common multivalue conversion table forthe C and M components shown in the Table 10 is referred to, then, asthe C component output value (C out), a value corresponding to thedensity value Ct is determined by referring to the multivalue conversiontable in Table 10, as C out=f(Ct), and as the M component output value(M out), a value corresponding to the density value Mt is determined byreferring to the multivalue conversion table of Table 10, as Mout=g(Mt).

[0303] After steps S740 and S750 or S760, the process ends.

[0304] Note that in this embodiment, “85” is used as the threshold value(Threshold).

[0305]FIG. 23 is a diagram showing threshold conditions regarding the Cand M components in the processing shown in FIG. 22.

[0306] Further, in the present embodiment, for the sake ofsimplification of explanation, a common table is used as the multivalueconversion tables f(Ct) and g(Mt), however, the common table is notnecessarily used but separate tables may be used.

[0307] Further, Table 10 merely has density values 0 to 255, however, asactual density values Ct and Mt may have density variation widths, whichmay differ in accordance with conditions of multivalue conversion meansand error diffusion method, about −128 to +383 at the maximum, thepresent invention is not limited to the values shown in Table 10. In thepresent embodiment, although the following values are not included forthe sake of simplification of explanation, actually unshown Ct(Mt) tablepart of “0” or less may have the same values of those in the Ct(Mt)=0multivalue conversion table, and unshown Ct(Mt) table part of “255” ormore may have the same values of those in the Ct(Mt)=255 multivalueconversion table.

[0308] Note that in the present embodiment, only ternarization ishandled, however, if the ink-jet printer as the image output device iscapable of handling quaternary or quinary representation by using dropmodulation and same-color various density ink (e.g. thin cyan ink, thickcyan ink, thin magenta ink and thick magenta ink), threshold tables formultivalue error diffusion processing such as quaternarization orquinarization may be generated.

[0309] Accordingly, in the above-described embodiment, even inconversion of multivalued image data into N-ary code, as the processingis performed by using a predetermined format threshold table, even ifthe threshold conditions are complicated, the processing can beperformed in a simple manner, and as the processing is simple, thecomplicated threshold conditional process can be performed at a highspeed.

[0310] Note that in the above embodiments, the liquid discharged fromthe printhead has been described as ink, and the liquid contained in theink tank has been described as ink. However, the liquid is not limitedto ink. For example, the ink tank may contain processed liquid or thelike discharged to a print medium to improve fixability or waterrepellency of a printed image or to increase the image quality.

[0311] The embodiments described above have exemplified a printer, whichcomprises means (e.g., an electrothermal transducer, laser beamgenerator, and the like) for generating heat energy as energy utilizedupon execution of ink discharge, and causes a change in state of an inkby the heat energy, among the ink-jet printers. According to thisink-jet printer and printing method, a high-density, high-precisionprinting operation can be attained.

[0312] As the typical arrangement and principle of the ink-jet printingsystem, one practiced by use of the basic principle disclosed in, forexample, U.S. Pat. Nos. 4,723,129 and 4,740,796 is preferable. The abovesystem is applicable to either one of the so-called on-demand type or acontinuous type. Particularly, in the case of the on-demand type, thesystem is effective because, by applying at least one driving signal,which corresponds to printing information and gives a rapid temperaturerise exceeding nucleate boiling, to each of electrothermal transducersarranged in correspondence with a sheet or liquid channels holding aliquid (ink), heat energy is generated by the electrothermal transducerto effect film boiling on the heat acting surface of the printhead, andconsequently, a bubble can be formed in the liquid (ink) in one-to-onecorrespondence with the driving signal. By discharging the liquid (ink)through a discharge opening by growth and shrinkage of the bubble, atleast one droplet is formed. If the driving signal is applied as a pulsesignal, the growth and shrinkage of the bubble can be attained instantlyand adequately to achieve discharge of the liquid (ink) with theparticularly high response characteristics.

[0313] As the pulse driving signal, signals disclosed in U.S. Pat. Nos.4,463,359 and 4,345,262 are suitable. Note that further excellentprinting can be performed by using the conditions described in U.S. Pat.No. 4,313,124 of the invention which relates to the temperature riserate of the heat acting surface.

[0314] As an arrangement of the printhead, in addition to thearrangement as a combination of discharge nozzles, liquid channels, andelectrothermal transducers (linear liquid channels or right angle liquidchannels) as disclosed in the above specifications, the arrangementusing U.S. Pat. Nos. 4,558,333 and 4,459,600, which disclose thearrangement having a heat acting portion arranged in a flexed region isalso included in the present invention. In addition, the presentinvention can be effectively applied to an arrangement based on JapanesePatent Laid-Open Publication No. 59-123670 which discloses thearrangement using a slot common to a plurality of electrothermaltransducers as a discharge portion of the electrothermal transducers, orJapanese Patent Laid-Open No. 59-138461 Publication which discloses thearrangement having an opening for absorbing a pressure wave of heatenergy in correspondence with a discharge portion.

[0315] Furthermore, as a full line type printhead having a lengthcorresponding to the width of a maximum printing medium which can beprinted by the printer, either the arrangement which satisfies thefull-line length by combining a plurality of printheads as disclosed inthe above specification or the arrangement as a single printheadobtained by forming printheads integrally can be used.

[0316] In addition, an exchangeable chip type printhead which can beelectrically connected to the apparatus main body and can receive inkfrom the apparatus main body upon being mounted on the apparatus mainbody can be employed as well as a cartridge type printhead in which anink tank is integrally arranged on the printhead itself as described inthe above embodiments.

[0317] It is preferable to add recovery means for the printhead,preliminary auxiliary means and the like to the above-describedconstruction of the printer of the present invention since the printingoperation can be further stabilized. Examples of such means include, forthe printhead, capping means, cleaning means, pressurization or suctionmeans, and preliminary heating means using electrothermal transducers,another heating element, or a combination thereof. It is also effectivefor stable printing to provide a preliminary discharge mode whichperforms discharge independently of printing.

[0318] Furthermore, as a printing mode of the printer, not only aprinting mode using only a primary color such as black or the like, butalso at least one of a multi-color mode using a plurality of differentcolors or a full-color mode achieved by color mixing can be implementedin the printer either by using an integrated printhead or by combining aplurality of printheads.

[0319] Moreover, in each of the above-mentioned embodiments of thepresent invention, it is assumed that the ink is a liquid.Alternatively, the present invention may employ an ink which is solid atroom temperature or less and softens or liquefies at room temperature,or an ink which liquefies upon application of a use printing signal,since it is a general practice to perform temperature control of the inkitself within a range from 30° C. to 70° C. in the ink-jet system, sothat the ink viscosity can fall within a stable discharge range.

[0320] In addition, in order to prevent a temperature rise caused byheat energy by positively utilizing it as energy for causing a change instate of the ink from a solid state to a liquid state, or to preventevaporation of the ink, an ink which is solid in a non-use state andliquefies upon heating may be used. In any case, an ink which liquefiesupon application of heat energy according to a printing signal and isdischarged in a liquid state, an ink which begins to solidify when itreaches a printing medium, or the like, is applicable to the presentinvention. In this case, an ink may be situated opposite electrothermaltransducers while being held in a liquid or solid state in recessportions of a porous sheet or through holes, as described in JapanesePatent Laid-Open Publication No. 54-56847 or 60-71260. In the presentinvention, the above-mentioned film boiling method is most effective forthe above-mentioned inks.

[0321] In addition, the ink-jet printer of the present invention may beused in the form of a copying machine combined with a reader and thelike, or a facsimile apparatus having a transmission/reception functionin addition to an image output terminal of an information processingapparatus such as a computer.

[0322] The present invention can be applied to a system constituted by aplurality of devices (e.g., a host computer, an interface, a reader anda printer) or to an apparatus comprising a single device (e.g., a copymachine or a facsimile apparatus).

[0323] Further, the object of the present invention can be also achievedby providing a storage medium (or recording medium) storing softwareprogram code for performing the aforesaid processes to a system or anapparatus, reading the program code with a computer (e.g., CPU, MPU) ofthe system or apparatus from the storage medium, then executing theprogram. In this case, the program code read from the storage mediumrealizes the functions according to the embodiments, and the storagemedium storing the program code constitutes the invention. Furthermore,besides aforesaid functions according to the above embodiments arerealized by executing the program code which is read by a computer, thepresent invention includes a case where an OS (operating system) or thelike working on the computer performs a part or entire processes inaccordance with designations of the program code and realizes functionsaccording to the above embodiments.

[0324] Furthermore, the present invention also includes a case where,after the program code read from the storage medium is written in afunction expansion card which is inserted into the computer or in amemory provided in a function expansion unit which is connected to thecomputer, CPU or the like contained in the function expansion card orunit performs a part or entire process in accordance with designationsof the program code and realizes functions of the above embodiments.

[0325] As many apparently widely different embodiments of the presentinvention can be made without departing from the spirit and scopethereof, it is to be understood that the invention is not limited to thespecific embodiments thereof except as defined in the appended claims.

What is claimed is:
 1. An image processing apparatus for performingerror diffusion processing on multivalued image data having pluraldensity components and outputting the result of said error diffusionprocessing, comprising: first determination means for, upon execution ofsaid error diffusion processing on a first density component among saidplural density components, determining a threshold value used in saiderror diffusion processing based on a density value of a second densitycomponent; first error diffusion execution means for executing saiderror diffusion processing on said first density component based onthe-threshold value determined by said first determination means; firstoutput means for outputting the result of execution of said errordiffusion processing by said first error diffusion execution means;second determination means for, upon execution of said error diffusionprocessing on said second density component among said plural densitycomponents, determining a threshold value used in said error diffusionprocessing based on a density value of said first density component;second error diffusion execution means for performing said errordiffusion processing on said second density component based on thethreshold value determined by said second determination means; andsecond output means for outputting the result of execution of said errordiffusion processing by said second error diffusion execution means. 2.The apparatus according to claim 1, wherein said first and seconddetermination means use a table showing a relation between density andthreshold values, for determining the threshold values.
 3. The apparatusaccording to claim 1, wherein said first and second determination meansrespectively determine plural threshold values.
 4. The apparatusaccording to claim 3, wherein said first and second determination meansrespectively use plural tables for determining said plural thresholdvalues.
 5. The apparatus according to claim 1, further comprising: thirddetermination means for, upon execution of said error diffusionprocessing on a third density component among said plural densitycomponents, determining a threshold value used in said error diffusionprocessing based on the sum of the density values of said first andsecond density components; third error diffusion execution means forexecuting said error diffusion processing on said third densitycomponent based on the threshold value determined by said thirddetermination means; and third output means for outputting the result ofexecution of said error diffusion processing by said third errordiffusion execution means.
 6. The apparatus according to claim 5,wherein, in a case where said error diffusion processing is performed onsaid first to third density components, said first determination meansdetermines the threshold value used in said error diffusion processingon said first density component, based on the sum of the density valueof said second density component and a density value of said thirddensity component, and said second determination means determines thethreshold value used in said error diffusion processing on said seconddensity component, based on the sum of the density value of said firstdensity component and the density value of said third density component.7. The apparatus according to claim 1, wherein said plural densitycomponents are a yellow component, a magenta component, a cyan componentand a black component, and said first density component is the cyancomponent, said second density component is the magenta component, andsaid third density component is the black component.
 8. The apparatusaccording to claim 5, further comprising image formation means forinputting the results of execution of said error diffusion processingoutputted from said first to third output means and performing imageformation.
 9. The apparatus according to claim 8, wherein said imageformation means is an ink-jet printer.
 10. The apparatus according toclaim 9, wherein said ink-jet printer has an ink-jet printhead thatdischarges ink by utilizing thermal energy, and wherein said ink-jetprinthead has electrothermal transducers for generating the thermalenergy to be supplied to the ink.
 11. An image processing method forperforming error diffusion processing on multivalued image data havingplural density components and outputting the result of said errordiffusion processing, comprising: a first determination step of, uponexecution of said error diffusion processing on a first densitycomponent among said plural density components, determining a thresholdvalue used in said error diffusion processing based on a density valueof a second density component; a first error diffusion execution step ofexecuting said error diffusion processing on said first densitycomponent based on the threshold value determined at said firstdetermination step; a first output step of outputting the result ofexecution of said error diffusion processing at said first errordiffusion execution step; a second determination step of, upon executionof said error diffusion processing on said second density componentamong said plural density components, determining a threshold value usedin said error diffusion processing based on a density value of saidfirst density component; a second error diffusion execution step ofperforming said error diffusion processing on said second densitycomponent based on the threshold value determined at said seconddetermination step; and a second output step of outputting the result ofexecution of said error diffusion processing at said second errordiffusion execution step.
 12. The method according to claim 11, whereinat said first and second determination steps, a table showing a relationbetween density and threshold values is used for determining thethreshold values.
 13. The method according to claim 11, wherein at saidfirst and second determination steps plural threshold values arerespectively determined.
 14. The method according to claim 13, whereinat said first and second determination steps, plural tables arerespectively used for determining said plural threshold values.
 15. Themethod according to claim 11, further comprising: a third determinationstep of, upon execution of said error diffusion processing on a thirddensity component among said plural density components, determining athreshold value used in said error diffusion processing based on the sumof the density values of said first and second density components; athird error diffusion execution step of executing said error diffusionprocessing on said third density component based on the threshold valuedetermined at said third determination step; and a third output step ofoutputting the result of execution of said error diffusion processing atsaid third error diffusion execution step.
 16. The method according toclaim 11, wherein, in a case where said error diffusion processing isperformed on said first to third density components, at said firstdetermination step, the threshold value used in said error diffusionprocessing on said first density component is determined, based on thesum of the density value of said second density component and a densityvalue of said third density component, and at said second determinationstep, the threshold value used in said error diffusion processing onsaid second density component is determined, based on the sum of thedensity value of said first density component and the density value ofsaid third density component.
 17. A computer readable memory for storinga program for executing the image processing method according to any oneof claims 11 to
 16. 18. An image processing apparatus for performingerror diffusion processing on multivalued image data having pluraldensity components and outputting a result of said error diffusionprocessing, comprising: calculation means for calculating a sum anddifference between density values of a first density component and asecond density component among said plural density components; M-aryconversion means for converting a value of the sum into M-ary code byusing a first function based on the sum; N-ary conversion means forconverting a value of the difference into N-ary code by using a secondfunction based on the difference; and execution means for executingmultivalue error diffusion processing respectively on said first andsecond density components, based on the result of conversion by saidM-ary conversion means and the result of conversion by said N-aryconversion means.
 19. The apparatus according to claim 18, wherein M andN are respectively a positive integer equal to or greater than
 3. 20.The apparatus according to claim 18, wherein said first function used insaid M-ary conversion means is represented in a first table showing arelation between the value of the sum and an M-ary code, and whereinsaid second function used in said N-ary conversion means is representedin a second table showing a relation between the value of the differenceand an N-ary code.
 21. The apparatus according to claim 18, wherein saidmultivalue error diffusion processing is executed by said executionmeans by using a two-dimensional table with the result of the conversionby said M-ary conversion means and the result of the conversion by saidN-ary conversion means as functions.
 22. The apparatus according toclaim 21, wherein said two-dimensional table is a common table for saidfirst and second density components.
 23. The apparatus according toclaim 21, wherein said two-dimensional table is prepared respectivelyfor said first and second density components.
 24. The apparatusaccording to claim 18, wherein said plural density components are ayellow component, a magenta component, a cyan component and a blackcomponent, and wherein said first density component is the cyancomponent, and said second density component is the magenta component.25. The apparatus according to claim 18, further comprising imageformation means for inputting the result of execution of said errordiffusion processing and performing image formation.
 26. The apparatusaccording to claim 25, wherein said image formation means is an ink-jetprinter.
 27. The apparatus according to claim 26, wherein said ink-jetprinter has an ink-jet printhead that discharges ink by utilizingthermal energy, and wherein said ink-jet printhead has electrothermaltransducers for generating the thermal energy to be supplied to the ink.28. An image processing method for performing error diffusion processingon multivalued image data having plural density components andoutputting a result of said error diffusion processing, comprising: acalculation step of calculating a sum and difference between densityvalues of a first density component and a second density component amongsaid plural density components; an M-ary conversion step of converting avalue of the sum into M-ary code by using a first function based on thesum; an N-ary conversion step of converting a value of the differenceinto N-ary code by using a second function based on the difference; andan execution step of executing multivalue error diffusion processingrespectively on said first and second density components, based on theresult of conversion at said M-ary conversion step and the result ofconversion at said N-ary conversion step.
 29. The method according toclaim 28, wherein M and N are respectively a positive integer equal toor greater than
 3. 30. The method according to claim 28, wherein saidfirst function used at said M-ary conversion step is represented in afirst table showing a relation between the sum value and an M-ary code,and wherein said second function used at said N-ary conversion step isrepresented in a second table showing a relation between the differencevalue and an N-ary code.
 31. The method according to claim 28, whereinsaid multivalue error diffusion processing is executed at said executionstep by using a two-dimensional table with the result of the conversionat said M-ary conversion step and the result of the conversion at saidN-ary conversion step as functions.
 32. The method according to claim28, wherein said plural density components are a yellow component, amagenta component, a cyan component and a black component, and whereinsaid first density component is the cyan component, and said seconddensity component is the magenta component.
 33. A computer readablememory for storing a program for executing the image processing methodaccording to any one of claims 28 to
 32. 34. An image processingapparatus for performing error diffusion processing on multivalued imagedata having plural density components and outputting a result of saiderror diffusion processing, comprising: analysis means for examiningdensity values of a first density component and a second densitycomponent among said plural density components; and control means forexclusively or independently outputting the result of said errordiffusion processing on said first density component and that of saiderror diffusion processing on said second density component, inaccordance with a result of analysis by said analysis means, wherein ifat least one of said first and second density components has anintermediate density value, said control means independently outputs theresults of said error diffusion processing, while if said first andsecond density components do not have an intermediate density value,exclusively outputs the results of said error diffusion processing. 35.The apparatus according to claim 34, wherein said analysis meansincludes: first comparison means for comparing a sum of the densityvalues of said first and second density components among said pluraldensity components with a predetermined threshold value; and secondcomparison means for comparing the density value of said first densitycomponent and the density value of said second density component witheach other, wherein said control means performs printing by said errordiffusion processing based on said first density component or saidsecond density component, based on results of comparison by said firstand second comparison means.
 36. The apparatus according to claim 35,further comprising third comparison means for comparing the densityvalue of said first density component with said predetermined thresholdvalue, wherein said control means further determines whether or notprinting by said error diffusion processing is to be performed not onlybased on said first density component, but also based on the result ofcomparison by said third comparison means.
 37. The apparatus accordingto claim 35, further comprising fourth comparison means for comparingthe density value of said second density component with saidpredetermined threshold value, wherein said control means furtherdetermines whether or not printing by said error diffusion processing isto be performed not only based on said second density component, butalso based on the result of comparison by said fourth comparison means.38. The apparatus according to claim 34, wherein said plural densitycomponents are a yellow component, a magenta component, a cyan componentand a black component, and wherein said first density component is thecyan component, and said second density component is the magentacomponent.
 39. The apparatus according to claim 34, wherein said pluraldensity components of said multivalued image data are respectivelybinarized by said error diffusion processing.
 40. The apparatusaccording to claim 34, wherein said plural density components of saidmultivalued image data are respectively converted by said errordiffusion processing into N-ary codes.
 41. The apparatus according toclaim 40, wherein said N is a positive integer equal to or greater than3.
 42. The apparatus according to claim 40, further comprising a tableshowing a relation between a density value and an N-ary code outputvalue, for N-ary conversion.
 43. The apparatus according to claim 42,wherein said table is a common table for said first and second densitycomponents.
 44. The apparatus according to claim 42, wherein said tableis prepared respectively for said first and second density components.45. The apparatus according to claim 34, further comprising imageformation means for inputting a result of execution of said errordiffusion processing and performing image formation.
 46. The apparatusaccording to claim 45, wherein said image formation means is an ink-jetprinter.
 47. The apparatus according to claim 46, wherein said ink-jetprinter has an ink-jet printhead that discharges ink by utilizingthermal energy, and wherein said ink-jet printhead has electrothermaltransducers for generating the thermal energy to be supplied to the ink.48. The apparatus according to claim 34, wherein said intermediatedensity is higher than an approximately half level of a maximum densitylevel.
 49. An image processing method for performing error diffusionprocessing on multivalued image data having plural density componentsand outputting a result of said error diffusion processing, comprising:an analysis step of examining density values of a first densitycomponent and a second density component among said plural densitycomponents; and a control step of exclusively or independentlyoutputting the result of said error diffusion processing on said firstdensity component and that of said error diffusion processing on saidsecond density component, in accordance with a result of analysis atsaid analysis step, wherein at said control step, if at least one ofsaid first and second density components has an intermediate densityvalue, the results of said error diffusion processing are independentlyoutputted, while if said first and second density components do not havean intermediate density value, the results of said error diffusionprocessing are exclusively outputted.
 50. The method according to claim49 wherein said analysis step includes: a first comparison step ofcomparing a sum of the density values of said first and second densitycomponents among said plural density components with a predeterminedthreshold value; and a second comparison step of comparing the densityvalue of said first density component and the density value of saidsecond density component with each other, wherein at said control step,printing is performed by said error diffusion processing based on saidfirst density component or said second density component, based onresults of comparison at said first and second comparison steps.
 51. Themethod according to claim 50, further comprising a third comparison stepof comparing the density value of said first density component with saidpredetermined threshold value, wherein at said control step, it isfurther determined whether or not printing by said error diffusionprocessing is to be performed not only based on said first densitycomponent, but also based on result of comparison at said thirdcomparison step.
 52. The apparatus according to claim 50, furthercomprising a fourth comparison step of comparing the density value ofsaid second density component with said predetermined threshold value,wherein at said control step, it is further determined whether or notprinting by said error diffusion processing is to be performed not onlybased on said second density component, but also based on result ofcomparison at said fourth comparison step.
 53. The method according toclaim 49, wherein said plural density components are a yellow component,a magenta component, a cyan component and a black component, and whereinsaid first density component is the cyan component, and said seconddensity component is the magenta component.
 54. The method according toclaim 49, wherein said plural density components of said multivaluedimage data are respectively binarized by said error diffusionprocessing.
 55. The method according to claim 49, wherein said pluraldensity components of said multivalued image data are respectivelyconverted by said error diffusion processing into N-ary codes.
 56. Themethod according to claim 55, wherein said N is a positive integer equalto or greater than
 3. 57. The method according to claim 49, wherein saidintermediate density is higher than an approximately half level of amaximum density level.
 58. A computer readable memory for storing aprogram for executing the image processing method according to any oneof claims 49 to 57.